We don't support TeX for the same base reason that we don't support uploading HTML, markdown, or reStructured Text files: They are all text markup formats, not media formats.

To start with, TeX files would likely be excluded from Commons by COM:SCOPE's prohibition on text formats. TeX files are also not paginated, so random access of a page would be difficult unless the file was converted to PDF first. I also don't know of any TeX processor that outputs images, so TeX files would probably have to be first rendered into a PDF and then thumbnailed. We would also have to decide what TeX distribution, packages, and extensions to support, which would limit our ability to process arbitrary TeX files.

I don't really see a use case corresponding to the required technical effort. The advantage of TeX files over PDFs would be that they're more easily editable. However, all or almost all TeX files would be works published elsewhere, and there are very few instances where those would need to be edited.