You are correct that taproot's "regular" multisig is more efficient than ecdsa multisig. This is mostly because schnorr signatures are usually about 8 bytes smaller than ecdsa signatures, and if you have (for example) 15 signatures, that adds up to about 120 bytes saved.

I don't know why more wallets aren't adding "regular multisig" (with taproot) as a feature. But if you want to play around with it, check out bitpac.org, which is one of my demos. You can use it to create a taproot multisig (not frost) using nostr keys and then spend it by having keyholders "vote" on what to do with the money. It wasn't hard for me to build so I don't know what other wallet developers are waiting for. But everyone's got stuff to work on, maybe it's lack of demand.