I am pretty sure that he's busy with about a million things. If you can do PHP and Symfony yourself, you can submit a PR, a fix, and then he'll review it and include it. If you can't, you can see if there's an issue filed on the issue tracker and if not, file one, and that'll put it in line for people working on PRs. It looks like it's up to about 400 open issues.

But everyone trying to drag his attention to their favorite feature in the hopes that he'll just go implement it really quick won't work. There's only one of him, and there are issues like the servers having trouble exchanging messages under sufficient load and patching SQL injection bugs (i.e. people turning up security holes) that are probably gonna be higher on the precedence list than QoL polish.

EDIT: Some other guy did submit an issue for notification of comments, and someone on that issue pointed out that they're already there. If you want to follow up on an existing issue, you could maybe point out that maybe the defaults for these should be changed: https://codeberg.org/Kbin/kbin-core/issues/293

I suspect it's off by default as part of the growing pains. It's probably a non trivial amount of work for a server to have to generate and track notifications. It is necessary though for non real time conversations.