Probably because... like any other business... niches develop and marketing is important.
Some women don't want a lot of clients, preferring high dollar, or maybe just less volume, in clientele. They can either make their money without marketing, as they have either word of mouth or referrals that take up the time they want to spend. Or once they establish themselves, they simply don't have to market, and they rely on proactive contact or regulars on longer term arrangements.
Some women don't want the additional exposure from the public, folks they might know, other providers, or authorities, and so they find that a UTR arrangement is good for them. Again, they don't have to market if they can make it up in UTR appointments and referrals.
In either case, better providers can maintain clients with a lower risk and hassle... so why not go UTR as long as they meet their personal business goals? I'm sure it's frustrating, but there is always a way! Unless a provider is just not seeing new folks (which happens) you can usually PM folks on their review list or any one of several ways of getting ahold of providers you want.
UTR ladies might also not be regular providers as well...if they want to move in and out (regardless of skill level), keeping UTR is a way to keep more permanent evidence from being around...
anyway... I just thought I'd reply, I'm sure there are multiple other reasons one can theorize, or providers can put out there. I'm just sharing the top of my head after reading
Just communicate via PM or ask around in places like the Men's Lounge, information is what drives this place, and if you ask, you'll be surprised what is out there!
Happy holiday week everyone!