There were a couple of recent-ish reports on here that claimed Poi Pet were refusing exit on the basis that the person would be denied re-entry.
Same situation as the OP, lots of Covid stamps. In one case the poster still had 1 of their 2 per calendar year land entries left but was still refused exit.
I don't know if the IOs who do this are being harmful or helpful. Perhaps they can sense that the 'perpetual tourist' only came prepared, funds-wise, for a quick out/in so if they let them exit, then what happens? How are they going to get to Phnom Penh and onwards with 50 baht and a packet of ciggies in their pocket? ????