Have you seen any providers on numerous occasions where the visits were good or even great, and then decline to a point where you don’t want to see them again?  

Not just in this field.  Someone starts seeing success and then realizes they can earn more for the same work.  Problem here, you already had a value in mind for what you paid.  Now, increase costs well above natural inflation and you get into a massive value loss.

One of the first FS providers I saw was a cute Asian-hawaiian young woman. Natural athletic body. Never rushed.
Then she decided to augment her breasts. Then her body kinda grew into the larger boobs. And her service became rushed, more transactional. Our last session was filled with little complications and interruptions and she even offered a steep discount for our next, but I never bothered to take her up on it.

I obviously don't know why.  He definitely doesn't like you though.  
The only reason I've ever just not responded to someone is because I don't like them as people.  
Ghosting is crappy. I just don't have the heart to say i don't like you.  

For me, it's happened every time. They get more comfortable and seem to want more from me and give less to me. It's like dating to marriage where you progress from courting and trying to win each other over to get me a beer honey and scratching your ass. Okay, not that extreme. But in my experience I have found most providers put a lot more effort into a new customer than a returner who they think they got a grip on.

For the first sessions, they were engaging and the service was first rate.

Years ago see this girl that gave massages and happy endings. Many times over the course of two years. At the time weed wasn’t legal where I lived. So I gave her money to get me some. lol totally scams me for the weed money . Im still baffled. She was super cute and have a great massage!  😢

Almost always.  Things start out great and then there is a personality change.  This is a very difficult business to be in and very few can do it for a long period of time without some type of personality change.

I tend to move on after XX amounts of visits. It mostly depends on how how well we click but eventually, I'll move on.
Its not her....its me

Never get too comfortable ladies. These gents have choices. I tend to be the exact opposite. I want to raise the bar for the next encounter because repeat business is the absolute best. I spend more time planning and preparing surprises for our next erotic adventure. I will do my hair, make up and select specific lingerie, and attire to arouse my play date. I want them to know that I know they could be with anyone, but choose me.😘

seeing them a few times this very question, i.e., do they stop seeing some regulars at some point and for what reasons?  I thought the most common reason would be developing real-life feelings, which makes doing business more complicated.  I was surprised that it was something else entirely.  The answer I got the most was, . . . . ."My business has grown to the point where I don't need to keep regulars who don't tip, so I gradually replace them with more generous customers."  Then they would usually add with a smile, "But don't you worry, you made the cut" or something similar.  Lol     (For the record, I tip everyone, even if I have decided during the session not to repeat.  It's the most personal of all personal services, like massages, manicures, haircuts, etc.)  

I have a provider I've been seeing for years, but for the last couple of months she's just phoning it in. It's nothing like it used to be, and I suspect she's getting burned out, or whatever.  

Sadly, it does happen.

and if they are good you get into the honeymoon phase.
Then you get used to each other and the newness and fun just aren't there anymore!

When I like someone and feel comfortable with them I tend to be a long term client.  In general, these relationships have been very successful.  I had the same FBSM for 9 years before retired.  The massage etc…was always excellent.  She did gain weight during the period but so did I!  For the last 18 months I have had a monthly appointment with the same woman who proves impeccable service each and every time.  It’s similar every time but so are most good things but the sameness issue can’t be avoided unless you change providers. My ATF is some I see in Vegas where we do longer  dinner  dates and I have seen her over 35 times in the last 4 years.  When you have has that many dates and spent that much time together sometimes someone is going to have less than their best day occasionally. I’ve had dates where I unfairly blame the provider because I was in a shitty mood or didn’t feel well.  
I do know that the relationship has soured when suddenly the provider in a rush and that two hour date is suddenly 90 minutes. That’s a real dealbreaker for me.  

I actually suggest when sessions start getting mundane just to take a break and see her again in a couple of months (depending on frequency it can be a few months or a few weeks). Sometimes a break is all it takes to rekindle and reignite interest.

Agreed.  I would take it further and say that if you get tired of providers all together, also take a break.  

It's been said on here (don't ask me to find the thread), that "three visits is the magic number" (paraphrasing).  Beyond three visits some providers (not all) will start to consider the client a regular and start to take them for granted.  I don't think that this is a conscious choice.  But, just human nature.

While a few providers started off strong and then faded, more often than not the experience remained strong and even improved over time.    That is why the average tenure of the gals I see is around 12 years.