> there's no delay inherent to playing back a recorded sound.

There absolutely is. You can decompress compressed audio files when loading so they play immediately, but if you want to keep your mp3 compressed, you get a delay. Games keep the sound effects in memory uncompressed.

> Not all sound effects are short

Long ambient background noises often aren't latency sensitive and can be streamed. For most games textures are the biggest usage of space and audio isn't that significant, but every game is different. I'm just telling you why we use uncompressed audio. If there is a particular game you know of that's wasting a lot of space on large audio files, you should notify the devs.

There is a reason both Unity and Unreal use uncompressed audio or ADPCM for sound effects.