As the matter of fact, soil is one of the least used substrate for planted aquariums. More people are using smaller gravel, sand, and other substrate than soil. Just in any online fish aquarium community you can confirm it.
It is simply easier to make a mess in the fish tank with ordinary soil as substrate. Vacuuming is not the only problem. Some bottom feeder fish will dig around too. Sure you can partially solve the problem by having a thick layer of something else on the top of soil, but it is just more troublesome if they get mixed up.
You may get away without vacuuming if you do not have a fully stocked fish tank. The accumulated organic waste will eventually cause old tank syndrome. It is really hard to keep the nitrate down even with a full tank of plants. Trust me on this. I had covered almost every square inch of the tank with plants yet the nitrate still go up as usual. The only way to prevent it is for me to have fewer fish.
Yes, priority plays a role here too. Some people see their aquatic plants more important than fish. So it is only natural they keep the environment more ideal for the plants. If the fish is your priority, nitrate should be as low as possible. Plants will do fine with even trace amount of nitrogen. You do not need to keep nitrate high just to please the plants.
