Doom scrolling wasn’t there in the early days of reddit. Lemmy is still new. I think people just had high hopes and expectations that lemmy would be a 1 to 1 replacement for reddit, but that was never going to happen. Reddit has had years to grow and optimize while lemmy is just a fledgling with a niche user base.
Also I think lemmy is missing that hook or gimmick to get, for lack of better words, the attention seekers here that will make posts and content just for upvotes or to show up on everyone’s front page. Not saying lemmy needs to be reddit, but I do think it needs a little extra something than just being a decentralized reddit alternative.