its not, just a very questionable idea from casters, in shooter games you arent forced to choose sniper in first game, grenadeer in second, heavy infantry in third and so on. Its bad for the sport (maybe good for fun), let them pick what they want.
Age of Empires II is not a shooter game though. I understand your point but as far as i recall, a lot of the top players like the fact that you can't just chose any civ you want in any tournament at any stage. I don't think that would make the games and series more entertaining, in the very contrast. It is a strategic game and the draft system adds another strategic element to it. Not everyone might like it, but i do believe it's way better for the game. Plus: Even if you don't like it as a player, it's part of the tournaments right now so if you want to do well, you better make the best of it. AoE is more than pick your civ and play the perfect game right now and i personally like that a lot but of course everyone can see that differently.