In Belgium There's a social security system that pays your wage when you're sick up a certain maximum. The first month(4 weeks) you get sick is fully paid by the employer. After that you get paid by social security for 60% of your wage up until a certain maximum.
If you are absent from work for 8 months ( cancer, surgery, burn out, ... ) you would be paid for every day you are absent, albeit less after a month.
While sick you are also protected from being fired. So employers can't fire you because you're out fighting cancer. It is mostly adhered to. If an employer would fire somebody who got cancer or because they got a burn-out/depression I'd probably find a different employer.
It's a good system, but with its own challenges ( abuse ). I honestly can't imagine having a fixed amount of paid sick days.
your employer can always "challenge" your sickness by sending a company physician, which they'd have to pay for. Some companies do it per definition, others never, some only when they suspect abuse.
How the US does not read this as: "I was bribed by the CEO of < company > to enact policies that benefit them" is beyond me.
Be better America.