Mastodon seems like a better comparison. It has more than a dozen forks and clones, and plenty of donation income.
Sure it would be good to have more contributions in Lemmy, but as these projects are made by volunteers they will do what they are most interested in. Nothing we can do to change that. And if they add new features which prove useful, they can also be added to Lemmy.
New users for Piefed and Sublinks are most likely to come out of the millions of Reddit users, not out of a few thousand Lemmy users. So this will increase the size of the Lemmy network and lead to more activity.