If you request a building/room by number, the CMs have no idea why you wanted it; was it because of the location, the view, the fact that there are elevators in the building, the smoking (or non) status of that building? And, even if they guess your reasons, they don't know which of those are most important to you.
Since each building is fairly small, and there are at least 3 types of rooms in each building, chances of getting the particular building you want are not that high. So, you have a better chance of getting what is important to you if you request the things like view, non-smoking, etc. Be sure to list the most important first, because the room assigners assume that you listed it first because it was most important.
Some of the buildings mentioned (like 64) are very highly requested because not only do people specifically request it by number, but it also fits into the highest requested categories (close to Hospitality House, close to main pool, close to bus stop, elevator buildings). So, there is a lot of demand for some of the buildings and only so much space.