For me it's the point that I don't know who is on the giving end. It could be someone who does it out of pure generosity, or it might be the "socially awkward" person that wants to fit in and gives away his last sats.

I haven't zapped a single person yet. I planned 1M sats for zapping as the maximum limit per year (plus the ones I receive). But the more I think about it the more it feels like that at some point it will be expected to zap. If you don't do it you won't be part of the cool kids. I've never been one of the cool kids.