Most Boomers aren't NIMBYs, but most NIMBYs are Boomers.
This is a thing that uniquely threatens them because their home is their primary investment, so anything that can be leveraged to keep prices high, they'll do. Environmentalism is usually the weapon they reach for, and because they have nothing but time, they have the advantage when it comes to a court system that privileges this kind of retireded spam.
>Social security
This is more because everyone under 40 or so doesn't trust social security will even be around for them to collect, so that group sees it, correctly, as an unfair wealth transfer from young to old. Combine that with the above, and combine that with the abject refusal to even entertain basic reforms (which goes double for non-US nations), and that's where the resentment comes from. Throwing good years after bad ones.