In my experience, ML folks submit to journals when:
Their work greatly exceeds the scope of 8 pages
They have been rejected multiple times from first- (or even second-)tier conferences
For the first reason, I think the best papers in TMLR are probably on par with (or better than) the best papers at ML conferences, but you’re right that the median could be worse.
Low-confidence take: Length might be a reasonable heuristic to filter out the latter category of work.
In my experience, ML folks submit to journals when:
Their work greatly exceeds the scope of 8 pages
They have been rejected multiple times from first- (or even second-)tier conferences
For the first reason, I think the best papers in TMLR are probably on par with (or better than) the best papers at ML conferences, but you’re right that the median could be worse.
Low-confidence take: Length might be a reasonable heuristic to filter out the latter category of work.