BIP 340 is getting plenty of work on The Nostr.

Honestly, as a programmer of bit twiddling algorithms both segwit and taproot obfuscate things a lot. Why couldn't the simple parts be separated?

Taproot especially. It's just deriving a new secret from a private key, with optional anything extra, using a sha256 hash.

What I want to know is why can't someone just let me directly use a secret key with schnorr and the bip 340 pubkey scheme? Like how nostr does?

Actually, you can, but for some reason the Bitcoin gods don't like a straightforward thing.

Secrets are just random big numbers. The signature algorithm doesn't care if you use the secret direct or hash it for no reason, as the taproot spec dictates. All still validate.