Re-entries, rebuys, addons are evil in my humble opinion. Even some pro players agree with it
Daniel Negreanu has been talking about reentry or rebuy in live tournaments, where, he argues, recreational players can often only afford to fire one bullet, but the pros can afford several. So reentry or rebuy tends to make the tournaments tougher.
Daniel did not talk about online tournaments and especially not the micro or low stakes tournaments, which most people play. And of course it makes no sense to claim, that a recreational player cannot afford to rebuy or reenter for 4$. He can and he will, so rebuy or reenter does not make online tournaments tougher.
In my opinion the most true form of tournament poker is the shootout. But a shootout mean, that everybody must pay the blinds and antes from the very first hand. If people can register late, then its not a shootout to me, and then I see no reason to limit reenter or rebuy either.
And realistically
poker sites are not going to get rid of late registration. It would be inconvenient for players, since they would need to wait for a new tournament to start, and as a result people would play less tournaments earning the sites less money.