The issue with large scale marketing is that it can be rather expensive.

Anyone can learn to code and contribute to Lemmy’s codebase, just like anyone can learn marketing. The difference is that it’s not so easy to, say, buy ad-space, get deals with content creators, etc.

Lemmy’s design, however, can be done by web designers, and it is done by web designers/designers, in part at least. For example, Lemmy.world’s icon was made by a regular user. That’s part of marketing I think (?).