If we're talking DVD's or CD's, both of which can be resurfaced when damaged, I'd say you have a point. But Blu-Ray, which current technology all but requires, can NOT be. To put this another way, if it's damaged, that's it, your game is fucked, the company MAY replace it, or they may not. And that's w/o considering load times.
Oh, the benefits that users would get from a switch to carts would be enormous. I mean, maybe not for every average user, but as a collector who has games ranging back from '77 in her collection, carts are my strong preference. Discs are comparatively fragile and can't really be fixed, the laser and moving parts inside the disc drive are finicky and wear down and break quickly and a repair usually requires buying pricey components if you're out of warranty. Just about every aspect of them ends up being a pain. And, yeah, load times and such, inability to save data to the game, etc. Meanwhile, the disadvantage for carts for me is that... uh... they can get dirty sometimes? I guess? So I'm rooting for carts, absolutely.
It's unfortunate that these decisions aren't made with what I want in mind! If they can manufacture games on a format that's cheaper to produce without upsetting consumers short term or damaging their brand long term, that's what will happen because as a company that's the perspective from which they have to view this. Which is why my thinking is that they'll only eat the cost of doing carts if they're fully embracing a vision of a shared library where one version of a physical game can be shipped to retailers which users can buy and play no matter which of Nintendo's devices they own.