Why do you think of Ad postings on public transport?

So I've started noticing these days that more and more buses are fully covered in Ads of private companies these days, even the AC buses are no exception, If I remember correctly earlier they used to post Ads only on the backside of the bus where a panel that's meant for ads is attached. If we consider the fact that most government buses aren't cleaned properly and they'll be dusty most of the time and to add more there are certain percentage of people who scribble on bus seats, damage windows and it's already messed up. To add even more to that now the buses have become poster walls for private companies. Shouldn't there be a restriction about where to advertise even if it's a bus? Especially a public transport which is meant for commuting is now becoming a moving advertisement banner. What's your take on this?