Because it adds to 'spam', I know you're giving out zaps and not asking for them but it is treated as spam on the feed. There is also a suspicion people do this (not saying you specifically are doing this, just a sentiment) to farm more followers with a goal for more zaps long-term.

Since you litterly bribe people for getting reach without delivering any real value. This is why. Since most people know, that knowledable people will find their follow naturally. So accounts who buy follows already think of themselves to not being able to produce any real value...