"Why does everyone use Fenders?"
'Why does everyone ask this question' is a reasonable follow up. This, and 'what bass should I buy?' are constantly repeated threads.
Not everyone does play a Fender, or any particular brand of strings, or amps or cabs, or anything else.
If you have a Warwick, and you feel you want a different look, or sound, or weight, or what-have-you, then off you go. There is a ton of great gear, and a pile of crap out there.
I have two basses only, both Fender P's, but that is just what I've come down to. In large part it is because they give me the sound that I am after. I never actually liked them much.
As it happens, I don't want to spend three or four thousand $ on a bass. It is also the case that I don't have access to a bunch of Spectors, or Foderas, or Zons, or Sandbergs etc. where I live. If I did, I might be playing something else. But the Hamer, the Steinberger, the EBMM Sterling, the Spector basses are all gone. I just play what my ears want to hear, and that is ideally what drives us all. And that is why there are a variety of manufacturers building different instruments; we all want to hear something specific.
Play what your hands want to hold, and what your ears want to hear.