They can't obviously just pick and choose who can and can't review them.

They can appeal to a client not to review them, but the client is free to do as he sees fit.

The ones that have many old but no new reviews most likely are mostly seeing their old regulars and not seeing new clients for various reasons.

for various reasons, and will ask clients not to review them.  If she already has them, she may decide she doesn't want any more, thus the reviews stop.  Not sure if she can ask to have all of them deleted without having herself delisted.  If she goes that route, she can't be mentioned on this site, as far as I know, and if you look for her, you will get a msg telling you that her information is no longer available here.

Swim

went to a different advertising venue...  just recently got a new review...   A provider can be voluntarily delisted but the profile is hidden as well as reviews & no reviews are allowed.  There are lots of legit reasons for this.  Sometimes a gal will retire for a period then, reemerge.  2 gals I've seen have seemingly stopped providing in recent months.  In both cases ads are gone & web sites down.