I've reloaded my New Vegas a couple times before with no problems, but the last time I did so I noticed that there are no folders in the data folder for textures, meshes, and so on, just bsa files with those names. This never happened before, and my Fallout 3 loaded just fine. Does anyone have any ideas??

Those folders are normally not present in a vanilla install, they tend to appear when mods are installed, disappearing as well if the mods are installed and removed by way of NMM.

Pretty much the same for Oblivion as well.

The BSA files are the folders, they're just compressed versions which the game reads instead. The only time you need to have distinct folders is when you're adding mods.

Are you saying your FNV is not loading properly? If so, explain with as much detail as you can.

Textures, meshes, sound, etc can be loaded from a BSA archive or as individual files. The latter are stored in the textures/meshes/sound folders. They can then be referenced from a .esp/.esm file or are used as a replacer.

Replacer files require archive invalidated to work. You can extract (decompress) all textures/meshes/etc from the BSA archives and store them in their respective folders. That is usually done by modders who want to mess with the

original textures or meshes.