I think I've heard a saying about this, something about premature optimisation...
Because it's well supported and solid otherwise? There's a wealth of documentation, resources of many kinds, software built around it (debugging, tracing, UIs, etc.). Because there's a solid community available that can help you with your problems?
What alternative technology is there that scales better? I guess MySQL could be it, but doesn't MySQL also come with a ton of its own footguns?
For a hobby project that might take off or might not, there's really no point in making everything "webscale"[0] just in case.