It's not about what they repair the most, it's about their knowledge, experience, and expertise in a niche. Even if they repair cheap household crap frequently, they may also make repairs on industrial equipment that's been in use for decades. They'd understand the differences between various products and companies, differences that a layperson wouldn't have experience with. They may not be analysts, but they'll know which models have expensive parts you'd need to ship from overseas, vs which models could be repaired with a trip to your local hardware store. That's the information that makes them a valuable resource.

I found this to be true for IT help desk. At the time I was doing this we saw a ton of Dell laptops that needed various repairs, and fewer HP laptops. However, we had no idea what the total breakdown was on campus between Dell and HP laptops.

Also, the Dell laptops we could almost always repair easily, they just needed a new hard drive or a new keyboard or something that was easily replaced. The HP laptops always seemed to need a much more complicated repair like a new motherboard or had to be sent back to HP.

So a naive perspective on this would be to say that we were constantly fixing Dell laptops, therefore those were crap. But we didn't have the full picture and the overall reliability determination needs to include both failure rates and ease of repair.