It's hardly ever a cabal or some group of elites conspiring in a smoke filled room. Landlords in general know that people are clamoring for something to be done about housing costs, most of them know that easing supply restrictions would be more effective in actually lowering rents than rent control, so they each on average fight hard against the actual solution and less hard against the ineffective one. Then the ineffective one is the one that passes.

It's the sort of false compromise that happens in politics all the time. Instead of solving the problem, you enact some alleged solution that really does nothing or makes the problem worse, but then politicians get to go tell the voters that they've done something. Then, when it doesn't work, they get to go back and pass another ineffective bill to "solve" it again in the next election cycle, meanwhile we get another four years of young people not being able to afford housing.

Most landlords I know want to ease building restrictions so they can build more rental units, and have a less expensive higher quality building than buying an old beater that they stitch back together again.