Junglers with high clear speed are actually able to be very gold efficient when jungling against bots because they don't have to worry about counter jungling, (being invaded or invading). They can simply go from one jungle to the next.
Top lane remains a solo lane because they still "need" all of the gold from that lane.
Playing against two bots is more annoying than challenging. They will zone you off pretty hard, especially if you do not have a lane bully yourself. However, this can teach you how to deal with a lane bully, which is a good skill to have.
Lastly, people don't like playing support in the bottom lane, ... so why would they want to play it in the top lane?
Honestly, what I would much rather see is bots jungle. I am very confident that Riot could make this happen in a way that would be at least somewhat effective. I think the concern is that bots would be incredibly predictable, which they would be. All they would need to do is ward. Bots are incredibly effective with "map awareness" because, ... well, .. they're robots. If they ward up their own jungle, they can react to an invade very effectively.