By and large, the two aren't particularly well matched. Bus companies sell the things they control - seat, ticket price, wi-fi etc - and livery is one of them - so their thinking is 'if we make the bus look nice, people will want to try it'. To them, it's a selling point (and on certain tourist routes it can be). Contrast that with how potential customers actually think, what they need to buy and how they have to go about doing it.
A customer will want to buy the bus as a solution to an immediate or future travel problem. And in order to solve that problem, they need to know/find out a number of things, including; who their local operator is, if they have a service that goes to the destination they require, what time it goes, what the best ticket is for the purpose of their journey, how they go about buying one etc. Hopefully, this information is available on a consistently branded website or app, making the whole information journey from non-user to bus user pretty seamless.
Then low and behold, the bus trundles along the road with branding that looks suspiciously like the purchase medium, with a large gleaming number on the front. Mr Joe Public puts two and two together and the bus operator has a new passenger.
So what part has the livery played in enticing the passenger to start the purchase cycle? At best, a limited one.
Of course, every bus operator should have a livery that is well designed and aims to make the product look attractive, but those two elements are no dealbreaker when it comes to solving the transport problems of a potential customer.
To them, the product's packaging is well down the list of importance.