Because there is a large impact of lead paint on the health and safety of many people who did not choose to put lead paint up on their walls, and children who did not choose to have parents who live in a house with lead paint, etc.
The reasons for regulations are for common standards where the market cannot enforce standards itself. I cannot understand in an extremely competitive market like London private hire transport, where not only are their competing apps and firms but excellent bus services, tube and overground services, TfL and the mayor decided to step in to pull Uber out of the market.
40,000 people out of work and over three million customers affected warrants more than the knee-jerk of "public safety" as justification. If Uber's standards were not acceptable to the public, who are the people that ultimately matter, then they would not have been so successful in London in recent years.
My hope is that this is just a gambit to twist Uber's arm and the arm is twisted - I think Uber getting banned from London is a very bad outcome. However, Uber improving its standards is a good outcome.