Yeah, even for extremely popular series, Tapas isn't an effective place to make money. They pay out a smaller percentage of ad revenue than their competitors, and ink donations, while slightly more effective, get a percentage eaten up in fees.
While it takes longer to unlock ad revenue on the likes of, say, Webtoon, at least once it's unlocked the earning potential is there immediately. Tapas unlocks it at such a low level that it's kinda misleading, people think they can start earning immediately, and that's just not the case.