You're not wrong, for sure. But I will take having only 1 app that could store my nsec over giving EVERY app access to it any day. The less possible points of exposure the better.
Looking forward to the day I can have my nsec on a tapsigner and even Amber won't be able to store it. (pls nostr:npub1az9xj85cmxv8e9j9y80lvqp97crsqdu2fpu3srwthd99qfu9qsgstam8y8)