Siege ladders have always been random and crappy. There's not really an excuse to keep them since they (1) go through walls (2) go over gates (3) can actually float right over walls (3.5) can actually float (4) can go to unreachable places (5) can float from one end of a keep to another, negating almost every defense (6) can be spammed to the point of defense being impossible (this one takes some coordination but, when it does happen, it takes all the fun out of defending).
The reason, so far as I can tell, that they aren't removed for reasons 1-6 is because it would change siege in an unpredictable way. That means a lot of work, testing, and re-design. The best compromise that I can think of is to limit it to 1 ladder per person on a map. This would likely handicap #3,5,6 and stop all but the most determined players from exploiting an underdeveloped mechanic. After that, some maps would need a few tweaks to remove the most common cases of #2,4. But as I said, this would take a lot of time and tiresome work from the kind volunteers that help make this game.