I think, in reality, in the modern era... it just comes down to the "set-up."
A massage parlor is street-front commercial property, with a business address and a business licence from the city.
An escort works out of private residential property, generally an apartment or condo, but sometimes a detached house, townhouse, etc.
At this stage... that is about it. That is the difference. The services are the same. Sexual services. That is what they are selling.
There is always a range of services, making things complicated to completely define. Some ladies are providing quite legit massage services, waxing, shaving, etc. etc. in a residential unit - but they also will do handjobs, or whatever - so they can be discussed here.
Alternatively, most of the big massage parlors are really more brothels than anything to do with massage. Massage can be provided if people want it, or skipped, or whatever. Handjobs, blowjobs and sex (or only some of those things) is what is primarily being sold.
But for the purposes of the perb board, I think they just split it up for ease of navigation. The traditional escorts (in an apartment/condo/house/townhouse) are in one section... and sometimes there is some "blurry" as to what gets posted there.... and the street front massage parlors, plus the ladies doing massage + handjobs (or whatever) in their homes, etc. are in another section.
it just makes it easier to navigate. Lots of guys would not consider walking into a street front place. Others love it.
"Real" (Registered Massage Therapist) massage providers that do not provide any sexual services CANNOT be mentioned here, and for good reason. We are reviewing and discussing sexual services here. The service has to have some erotic or sensual element at a minimum to be discussed here... as I understand it.