The first versions of the Unreal Editor didn’t really have an asset viewer, just separately windowed lists of textures, meshes, sounds. Once they moved over to a unified “asset viewer” they didn’t have an easy way to sort by type, only name, so artists at Epic started adding the prefix. Sorting by type was added eventually, but by that point it had already become a standard practice, plus if I remember correctly you couldn’t have two assets with the same name even if they were different types. Since all of the assets that came with the engine were using that naming scheme, most studios adopted it (or something similar). Over time some have stuck with it out of familiarity, and others don’t either because new people come in whom don’t have that practice ingrained into them, or for no real reason at all.
Personally speaking, I’m terrible with naming schemes. Nearly every project I’ve ever worked on has used a slightly different naming scheme, with and without prefixes, camel case or underscores, etc. At this point I tend to just dump all of my stuff into one big folder with every other file using a different naming scheme and at some point I might do a pass at unifying it only to completely forget what I’d decided on for the next asset I make. It doesn’t help that every project I’ve been on they’ve changed the coding style guidelines too. 