My understanding is that the ~/Library/Audio/Presets directory is created and used by Logic and GarageBand for storing Audio Units presets (.aupreset). Eventide presets are stored in a custom format (.tide) that can be used by all the plugin formats we support, so we made the decision to use a different location.
That is where almost all other developers put their user presets, .aupreset or not. U-he, Valhalla, Softube. It’s mostly only Native Instruments, iZotope and Eventide who do not.
Default presets usually go in /Library/Audio/Presets: