I would imagine there is the thrill of the hunt as well.  Part of the thrill of the hobby is seeing different people and sometimes seeing what you can get that is NOT offered.  If you become a regular at a massage parlor lady, which is far less cost than a regular to a provider, maybe the massage lady will provide something extra.  If not you are getting a quality massage at minimum.

I do not follow the busts all that closely, but how many of the parlor busts have been a non Asian place?

Then there are the sensual massage ladies...DiY is the primary, but what if?  A lot of very pretty senual massage ladies and I have noticed a number of them switching to providers.  Being the FIRST in line to that switch is always FUN!  Like a first time fuck with the gal you met next door or in the bar, at the beach, you get my point!

There a LOT of options in the hobby ALL come with some risk!

With rates of $60-70-80 at most AMP's and being able to just walk in spur of the moment, it's the perfect place for a gentleman on a budget that doesn't want an escort and can't  plan ahead of time.  
Also, there's several ladies to choose from on the spot.
 Guys love their variety and some have their preference set to  only seeing Asian women.
Have you ever had a table shower before? Omg, they're awesome! I can totally understand how that can get very addictive.  
 Besides that, these places are being run legitimately and are licensed . That whole being trafficked for sexwork "rescuers" spew to the media is complete nonsense for the most part ( from first hand experience.)  
I'd say one isn't at any more risk going to an AMP than an escort & that it just boils down to simply being in the right place at the wrong time which is true for all sides of the hobby even if we screen the heck out of people .

I actually enjoy  a decent massage after/before release.