Hmm; not sure about legality aspect, but in many places where Uber
is perfectly legal and common, the drivers have nevertheless asked me to sit in front due to fear of violent reaction by Taxi drivers.
In the city I'm currently in, Taxi drivers and unions have used various means to create political pressure - from peaceful protests; to aggressive protests; to attacking Uber drivers; to attacking their offices (they also apply the same tactics between each other when a different taxi company wins an airport license, etc.
(Oh, the city is Ottawa, the capital of Canada).
Note as well, Uber was "illegal", in the sense that there's no framework or license under which it operates, pretty much everywhere it started, and in many popular places still is. It entrenches, and then fights to become legal. You probably used Uber "illegally" (as in, operating outside of framework of existing law and regulation framework) before, without being so explicitly told or aware.
(and while this is not a message likely to be received well, and I genuinely mean it with best of intents - if you are a person with limited local language skills or awareness traveling alone, and if you are not willing to take risks, this is a good lesson to do research before landing. Much of the world is NOT equally tourist friendly, and nowhere is Ignorance of Law a permissible defense :( )