Since the dawn of aviation, people haven't been getting their first choice. Even loading a few more of each dish, you'll still have people in the back row not getting their choice. Load one of each meal for each person, you'll have immense waste, and still people won't get the meal they'd really like. You can also bet that today's flight will "sell out" of dish A, tomorrow will run out of B, and yesterday it was dish C that was most popular. You could instigate an online reservation system, but guaranteed every flight there will be people that didn't know such a thing was possible, and not get their first choice.

If the meal is very important, talk to the crew ASAP to reserve your choice, and they'll probably put it to one side, especially for a Gold towards the back of the cabin.