For forums it can be easily removed because you can give forums a name so they no longer show the ID.
For threads and posts unfortunately it's pretty fundamental to the way forums work and there's no difference here between that and every other piece of software (not even just forum software). Each URL needs to identify its content uniquely, and the way that happens for posts and threads is it includes the thread and post ID in its URLs.
Any other way just isn't feasible.
And it won't be hurting SEO. Poor content. Poor discoverability. And many other things affect SEO. Numbers in URLs doesn't
And actually, sometimes it's just more fundamental than that: Google sometimes changes their algorithm. If they do that and it affects how often or what it crawls on your site, or what results of yours it returns: tough luck