Third party accessories appear when a product is big enough to warrant them. Most Nintendo gaming systems have achieved that level of success. Nokia phones regularly achieve that level of success. The tablets saw screen protectors, automotive mounts, and cases, but never grew large enough to spark an explosion of accessories.

You can fault Nokia for not advertising the tablets, though that appears to have been by deliberate design, but it's not as though they actively prevented other companies from producing accessories.

As for NOA's repair service during the era of the original Game Boy, I wasn't overly impressed. When our NES died, we had to drive two hours the nearest authorized repair drop-off point--a kiosk in a mall--and return a few weeks later when the repair was finished. My last name and old address are still scrawled in black marker on the bottom of both controllers and the console itself, as the kiosk employee warned us that Nintendo often lost units otherwise.