Why? Professional domain squatters are the ones that never forget to renew, because it's their main business. And if they stop paying on 1,000's or 100,000's of domains, the registrar will take them to court pretty quick to resolve the contractual debt. And either the company goes bankrupt or pays the bill, same as literally any other professional service. A contract's still a contract.
And if you're squatting on just a few domains personally and stop paying, it goes to collections, shows up on your credit report, and lowers your credit score like any other consumer debt not meeting payments. Which, if you want to open new credit cards or buy a house, is gonna be a big problem.
There are already avenues to address this, the same as any other debt you incur. "Forever" just means until it sends you to bankruptcy and you lose it formally, worst-case scenario. It's not some kind of blank check to register a billion domain names, not pay for them, and face zero consequences...