The biggest thing is that most other mining coins are based on PoW for verifying transactions on the blockchain. The PoW is heavy because it needs to be for security. IOTA PoW is light because it's not worried about double spends. The iota PoW is about preventing someon from giving their own branch enough weight to write its own transactions.
Mining monero via coinhive is not only resource intensive but it's also in competition with legit mining pools