A bunch of reasons:

- Can be faked (at least two ways), skewed incentives: #[1]

- PR was rushed, feedback was ignored: https://github.com/nostr-protocol/nips/pull/224#issuecomment-1429286164

- Fragile design, not interoperable with paid relays or client auth: #[2]

- Easy to DDoS zap receivers = encourages centralization of LN nodes: #[0]

- Much less private than LN sats

- Requires LNURL changes (not interoperable with plain LN / LNURL, no graceful fallback)