This kind of change is widely unpopular - not because people don't think a change should be made, but because this is a very "meh" kind of change.
Yes, the current system is somewhat unfair to those users who never get upvotes but frequently get accepted answers. They essentially never make any progress like those users who do get upvotes on their answers and experience no problems. However, starting to count accepted answers into the equation doesn't solve the problem. All it does is shift the problem in the other direction. Now those users who only ever get accepted answers are making progress, but those users who do get upvotes are essentially doubling their progress for no apparent reason.
And therein lies a bigger problem. This change potentially makes it twice as easy to get the tag badges. If tag badges didn't mean anything like the others, we frankly wouldn't care, but gold tag badges give users heightened privileges on questions with that tag, and we have to be careful not to make it too easy for that privilege to be obtained. Allowing this change would likely mean we'd have to modify the criteria for the tag badges to make them more difficult to obtain based on the new system, so any progress you'd make by counting the accepted answers would likely be diminished by the increased criteria for the badge.
As said before, this kind of change doesn't solve the problem at hand. All it does is increase the benefit for a minority that have trouble getting upvotes on their accepted answers, when there is probably a much better solution out there somewhere that doesn't overcompensate another minority.
