Why is reading/writing memory cards slow in PS1 emulators?

Speed of flash memory and other storage has improved quite a bit since the PS1 days—and now some emulators can provide higher-than-native reading speeds when loading a ‘CD’ in a game (e.g. PS Vita's built-in PSPEMU can do this). However, somehow this hasn't affected the speeds of reading or writing a PS1 memory card, in all emulators that I've used. Detecting a memory card is slow, writing it is slow, reading it is slow—even when the game clearly doesn't reload the game world but just reads a few numbers. Considering the minuscule size of PS1 saves by modern standards, they should be read or written in moments.

I'm curious: what limits the speed of PS1 memory cards in emulators?

It vaguely seems like games are doing some low-level electronics with the cards, instead of delegating to the console's API—so the emulator has to preserve the original timings and can't hijack the goings-on with a faster approach. If this is the reason, then how widespread was this method of talking to storage, in those days? And was it carried into the PS2 generation or later on?