-snip-
What makes it unsafe for Electrum to generate seed phrases itself? Does it have something to do with not being able to clear the memory they were stored in?
BIP39 has several weaknesses that are almost similar to the seed phrase model that Electrum used before version 2.0, in this case, about using bidirectional encoding between seed phrases and entropy.
Electrum can still import BIP39 seeds, as I have mentioned before.
However, the developer does not recommend it for several
reasons, as the link o_e_l_e_o has shown.