It was removed from public display because to some extent it only encouraged comments nagging the OP to improve their accept rate while providing no other useful guidance. While in theory I agree that the info is nice to have, the way the system displayed the accept rate (in percent, colorized) made it appear like an accept rate of 100% was the only desirable outcome, which simply isn't true.
Before continuing, here's the relevant Meta Stack Overflow question: Let's stop displaying a user's accept rate.
I would also like to add that there's really no effort required to mark an answer as accepted. It literally takes a fraction of a second. Even more so, users should never be forced to accept answers just because the community thinks accepting answers is necessary. This is not the case.
Granted, new users should learn that answers which solved their problem should be accepted, but once a user knows how to accept answers, they should never be forced to do it.
A user with 0% accept rate indicates a problem, but the way the community dealt with this was often more than rude or not constructive. Politely asking them whether a solution worked for them and if so, telling them that answers can be accepted is the way to go. But this is something you should only tell them once.
And quite frankly, I don't see an issue with answers not being accepted as long as they are voted on and thus deemed helpful by the community. It's not the 15 points or the green checkmark that matter in the long run.