Reddit has been declining for years as well and basically just lives on momentum from earlier days when forums or forum-likes had their heyday.
Lemmy is trying to get a cut of a shrinking user base and is doing so by being a very close copy of Reddit. It’s not exactly surprising that it only “grows” when there is a wave of people annoyed with Reddit for some reason.
Your suggestions are fine, but the internet as a whole is moving to semi-private communities and Lemmy is not going to stop that overall trend.