And why not, if you know what you're doing and particularly if it's not "internet-facing". Lots of internal systems will continue to run happily for years with Python 2.
New projects, however, should be done using Python 3 unless you have a good reason not to do so: I know of a couple of libraries that are Python 2 only, largely because the developers have not had the time to port them to Python 3. I suspect that, where the need is great enough, other people will take on the work either, where the source is available, or a clone where this isn't the case. This has happened in the past: Pillow replaced PIL after it was effectively abandoned.