pull a NCNS on them.

LLAP,
Swim

same reason you want to know when you are getting your check..

Either you created a doubt in her mind that you aren't going to go through with the meeting, wants cut her losses on you, and doesn't want to spend more time on a meeting that isn't going to happen,

Or, she is running a bit late because of her day job, traffic, another appointment, and needs some extra time to freshen up.  

When I've done an outcall, I like it when a lady lets me know she's on the way, or if there are delays.  Shows me respect for my time.  I pay it back by updating my status as well.

-- Modified on 6/30/2017 9:09:26 PM

It is just polite...let's her time herself to make sure that she is ready for you.  It is also a way to reassure her that you are actually coming...for those who do not come after stating they are on the way etc, well, they are jerks which are commonly known as time wasters on this site.  

Also I personally anticipate and fantasize before my date arrives.  Just like your visual movie is playing in your mind's eye, so is mine.  Sometimes I pleasure myself before a meeting if I am particularly aroused or deny myself in preparation.  

I am never just sitting around waiting for the phone to ring. If you are running behind, it gives me time to  answer texts/emails/phone calls, stop for gas, mail something, finish a project, exercise, clean up a mess... whatever is on my plate at the moment. If you are not coming, I need to know right away so that I can go on with my day instead of sitting around waiting for something that may never happen.