Comparing to session IDs, you have no way to know if an unique id is bogus or not. You have to check from a list, be it a cache or a database. This limits the scalability of the solution. I'm not an expert, but AFAIK JWT verifier can be stationed on the edge of the application network, and I have not checked this but I suspect they can even make a hardware solution for those kind of activity. That's definitely a big reduction of attack surface in terms of DDOS.
IMO JWT doesn't have that many moving parts. Encryption parameters are handled by libraries according to tested standards. The only real thing you need to do is to keep your private key safe.
So you have to check a signature, right? Maybe this is what the other commenter meant when mentioned encryption.
Session IDs don't have any of these problems. It does mean you have to do a database lookup on every request, and that can cause problems with scale, but if you have to hit the database anyway for other reasons then you have that problem anyway and have to solve it for those other reasons.
I guess DDOS attacks - if we're checking the session ID on every request then that's a potential attack if you just make up uuids and throw them at the server.
But JWT's themselves are an attack vector, surely? If there's any mistake in the encryption (or any vulnerability in the libraries used) then this is a door open very wide indeed.
The beauty of session IDs is the simplicity of it - very few moving parts, so very few opportunities for mischief. JWTs seem to be the opposite: lots of moving parts, lots of opportunities.