Confirming whether or not the BIP39 checksum is correct also requires the importing wallet to have the exact same word list as whichever wallet generated the seed phrase in the first place. While there is obviously a set word list which all BIP39 wallets use, this does mean that the word list cannot be changed in the future or it will no longer be compatible with current seed phrases. It has also posed problems with people generating seed phrase in languages other than English.

Electrum seed phrases, on the other hand, do not require a fixed word list and do not require the importing wallet to know the word list which was used to generate the seed phrase in the first place.