why would they want to avoid being complaint with a standard. That doesn't make any sense.
See here:
https://github.com/spesmilo/electrum/pull/6001It helps prevent some confusion. If a user is unaware of the difference between Electrum and BIP39 seed phrases (as many are), generates a seed phrase on Electrum which happens to also be a valid BIP39 seed phrase, and then imports that seed phrase in to another wallet, they will end up recovering an entirely different wallet with entirely different addresses.
Electrum seed phrases contain a significant advantage over BIP39, which is the version that pooya mentioned. When you recover an Electrum seed phrase, Electrum knows exactly what type of wallet (legacy or segwit) to recover. When you recover a BIP39 seed phrase, you also have to know which type of wallet you want to recover, some wallets and services do not give you an option or do not support all types, many users don't know the difference, etc.