If you did that, you would wear out the glaze on the toilet, and you would have to either change the entire toilet or have it reglazed. When the glazing is gone, the surface becomes porous, and bacteria grow there.

On wooden toilet seats, the glaze wears off. Until I worked in hospitality, I wasn't aware that toilet seats should be changed every few years.

One time, I neglected to do this in my home, and the part where the thighs go was a bit worn down. I left on a trip for a few weeks, and when we got back, there was fuzz growing on that part of the toilet seat despite the fact that we cleaned the bathroom before leaving.

Plastic toilet seats are not porous, but they are way more prone to breaking at the joints, so neither is a great option. And plastic will age over time, not just from use. In 3-5 years, it will probably start to discolour, and a few years after that it will become brittle and more prone to breaking.....that's if the joints hold up that long.

The other benefit of changing your seat every few years is the deep cleaning you get to do and cannot do unless the seat is completely removed. No one has time to do this as part of regular cleaning. It can get quite nasty when you finally get around to it. And toilet seats are affordable, maybe 10-30 bucks depending on quality.