I think it has more to do with the doctor thinking about the absolute nightmare they are going to have to deal with interfacing with insurance companies trying to treat you. The dismissal is just their self preservation.

I have noticed that a lot of their job is playing insurance games to treat (get past preauthorizations) easily documented health issues, let alone things like ME/CFS or long COVID.

That’s a US-specific problem. Doctors dismiss patients’ complaints all the time in countries with universal healthcare.

I think the issue is much simpler than that: if the doctor is out of ideas (and doesn’t know of a specialist to refer to) they just get frustrated and give up.

I am in the process of recovering from CFS (currently back to working 100%, though still not being where I want to be with everything else) and at no point my doctor has done anything but take it seriously. Of course, a doctor can only do so much with a disease as nebulous as this, but he (as well as work, family and other people around me) giving me breathing space and adapting to my situation has been crucial for my improvement, I'm pretty sure.

Good to hear, several people around me did not have that experience with covid, but sure there must be good doctors.

It is, in general, a poorly understood disease (as lots of others in the thread are pointing out). And everybody's case is different.

I will point out that I've never gotten so much unsolicited low-quality advice before, though; people who barely know me will make a very confident diagnosis on-the-spot once they hear I've got a long-term illness. E.g., “you're vitamin D deficient” (no, I'm not, and anyways, I've been taking vitamin D supplements for three months just in case, with no effect). I'm sure they mean well, but it becomes tiring really fast when everyone does it. (There's a select few people who seem to be much more careful about throwing our random crap like that, including, unsurprisingly, all the doctors I know.)