Would you buy a console without turning it on, popping in an online-ready game, and attempting to go online?
Nintendo should start adding some bright, easily visible message to the system UI that indicates the device is permanently restricted so that buyers doing a cursory check would see it. It should be as obvious as a theft-bricked iPhone.
I believe they have a financial incentive to not do this. If buying a second-hand switch is perceived as risky, then sales of new switches will be encouraged. Of course this would cause a switch to depreciate even more when you buy it since it would suppress the market price of a used switch. But I'd wager most people aren't considering how much they could get from selling their switch when they're considering buying one.
Alright I'm claiming ignorance here; I didn't know you had to play an online game to know. Figured it would tell you as soon as it came up assuming you were near wifi (which even then is a big assumption.) My mistake, hadn't thought it through.