considering how horrible vtf compression is I can understand using bigger textures. From what I recall most weapons use 2k

The key word here is surface area. Most other weapons represented in the game consist of simple rectangle or cylinder shapes that are easy to chop up flat onto a 2D image. However, when making more organic shapes, things won't be so simple anymore. Irregular and concave objects, like vertebrae, require a lot more texture space around them than a steel barrel. This particular example also has 17 identical segments, with 16 more in between.

I could pack it all onto a single texture. And I could reduce the resolution to 1024. But then it will be a minecraft weapon. I think slightly above average file size is a reasonable tradeoff to make something SFM- and viewmodel proof for years to come.

Oh, and 37MB is not what will be in the game. That includes all the uncompressed original files so valve can recompile the weapon if needed. Packed to a .vpk the actual game files are a fraction of that.