Thing is the high earners who actually put in more than they take out don't need 'free' bus passes, because they were high earners. If they need one, it's very likely they were net 'takers' from the system, which is fine and dandy, but let's not argue that they are owed a bus pass because of contributions.
^ this.
With RTI (real time information) that DWP gets for all claimants from HMRC, as well as richer data from bank transactions, means testing is not difficult or costly like it was 5 years ago. The reason the government haven't removed bus passes, TV licences etc. from the older population is purely down to votes. Older people are more likely to vote, ergo they must be kept happy. Until younger people actually go to the polls in significant numbers we will always end up with crappy policies that benefit the older generation.