This is due to the design of the Switch and the dock in which Nintendo did not offer any kind of protection or padding, and also because instead of choosing to use something more sturdy like Gorilla Glass to cover the display, they chose to use plastic, which means that it is easily scratchable, especially if you were to slot it in and remove it constantly and if you’re aren’t being very careful about it.
Like we said investing in a screen protector is probably the best solution at the moment, although there are more creative solutions out there on the Nintendo Switch subreddit where some users are adding adhesive foam padding along the rail area, while others have suggested placing a microfiber cloth which might be better as it is thinner than the foam.
We’re not sure why this isn’t something Nintendo hadn’t considered, or maybe they did and in a bid to keep costs down they decided not to do anything about it, but either way hopefully future generations of the console will address this problem.