In general top laners are champions that can hold their own in a 1v1 matchup while being able to farm up in lane reliably. There typically isn't much action top lane. A big reason for this is that until recently there wasn't really an objective like Dragon to take. So top lane has not been of much importance until Baron spawns at 20 minutes. Even with the addition of the Rift Herald in the top lane not much has changed. It does give a bit more incentive for junglers to head top lane so they can get that buff for their top lane and deny it from the opponent but does not change the types of champions that go top.
Champions that go top should also be something that fits into your team's composition which is why the top laners are usually tanks and fighters. Since you have ADCs go bot with a support (explained in this question) and APC in the mid, that leaves your jungle and top laner to fill out the other roles on the team.