I am guessing that a lot of lightning addresses are not set up yet to send zap notes back to nostr. So that would probably account for the discrepancy between sent/received.
It wasn't until just recently that I got my own lightning address set up to sent zap notes to Nostr upon receipt, I know that.
This. Not all wallets support Zaps, though we're getting more added all of the time.
Ya, personally using Ligess for my lightning address and they have a pull request I had to fetch to add zap support. Still early and hasn't been fully released yet. Working great though. Lots more support for zaps to come hopefully!
