Social security has a max payout, so it also has a cap on the taxes you pay into it.

At a surface level, it makes sense, which is why it continues.

Once you look into it even a little bit further, the max payout needs to stay, but the tax cap needs to be removed.

I'm pretty sure they are. The more you pay into the system, the more you get at retirement age. But, it's also capped. I'm assuming that's the rationale behind capping the tax.