I don't know how many of the wanted it but here is an article that talks about it. Atleast is New York City they were forced to implement it and then it expanded from there.

> Uber might finally be forced to change its tune after New York City's Taxi and Limousine Commission introduced a proposal this week that would require ride-hailing companies operating in the city to allow riders to tip their drivers. The need to follow a rule like that in one of Uber's biggest and most important markets could force the company to allow tipping across the country or around the world.

> The Independent Drivers Guild lobbied for the New York proposal, which it estimates will lead to over $300 million per year in tips for New York drivers.

https://mashable.com/article/uber-nyc-tipping