Well, the actual reason that they dropped all those things is totally different. Cars and buses are mostly because of how much more expensive it is to get the proper vehicles from junk yards. If they can cut 20+ cars down to under 10, they actually save quite a bit of money. Besides, ever since 2010, Monster Jam's tracks have been utilizing cars less and less up until when the first all dirt tracks started appearing in 2014 (i.e. Oakland), before BKT's had even been made. As far as containers, they haven't been used for anything other than backflip ramps since the first one at World Finals 12, and are still used as of this year for that same reason (Backflip ramps at World Finals 17). Campers are mostly gone because of the danger that they caused. The stray parts that came off when they collapsed had actually flown into the stands a few times so Monster Jam cut them. All this has to do with the safety and cost efficiency of the show, rather than the BKT's. Most all of this actually happened before BKT's came along anyway.
So why do they use them? Yeah they have a weak sidewall, everyone knows that, it could be better. However, they have a contract with BKT requiring them to be used for sponsorship reasons, and they can't just say "no" without having to take large legal steps that aren't worth it.
And just to throw it out there, the reason they have such small treads/handle poorly is because the big cleated tires (Firestones/Ukraines) were actually so grippy that they would throw dirt and rocks into the stands in some instances, and were also causing damage to the stadium floor in a lot of cases. Monster Jam actually disallowed the cleated tires from running before the BKT's became mandatory for this reason. Any cleated tires had to be shaved down. You can tell if you look at the treads of Ukraines toward the end of FELD's use with them. They were significantly shaven down compared to how they used to be.