Buses need much less lanes since in dense areas one bus line can serve thousands of ppl that live close to each other. Operating buses on all roads is not practical, it'll be expensive taxi on steroids, the scope of the bus is to collect ppl from a bigger area and drop them to a place where ppl also continue walking to their destination
Is that true on a like for like basis? E.g. a car goes to my house. A bus needs the same road that cars do.