If people don't want to play the games again they don't have to, but this makes those ports available for the soon to be 70-100 million Switch owners that didn't own a Wii U. Nothing wrong with those people having the option to play old Wii U games on their current device.
Not like those ports took a lot of effort, devs, or time. Switch basically is the same graphics level as Wii U with slight enhancements made. Just like Wii was to GameCube. They only truly upgrade power/graphics every two generations, so I suspect Switch 2 games will look significantly better than Switch 1, which also means if they port Switch 1 games over to 2 they will look noticably worse than Wii U games look compared to Switch.