No, it's certainly not just BRP. Had the same problem with my previous bike, a 2006 Kawasaki Vulcan Mean streak. I purchased it in 2018 with only 7K on the clock, and it looked like it was just rolled off the showroom floor. I ended up with a leaky front fork seal, and the local Kawasaki dealer wouldn't touch it. Had to take it to an independent shop.
While I too was miffed that they wouldn't work on a bike because it was over ten years old, despite it looking nicer than a lot of under ten year old bikes I've seen, I cooled off and thought about it. Having worked on older vehicles myself, regardless of their condition, plastic and rubber becomes brittle with age, fasteners can corrode at the threads, not only making them a bear to remove, but also more likely to take threads with them or to snap off in the case. Fiddling around older wiring can losen connections that may look fine, but are marginal. I determined the ten year rule was likely to prevent a simple repair turning into a more complex and costly one where the owner gets upset at the rising cost and stuff the mechanic "busted" while working on the bike. I think of it a bit like working on old plumbing. It may look fine on the outside, but once you start wrenching on it, a simple job can turn into a nightmare. Also the older the bike, the more likely the owner has "tinkered" with it or modified things. I've encountered some of these mods myself. As an example, while not bike related, when we bought our house last year we decided we wanted to swap out the fan switch in the bathroom with a timed switch. The fan switch and the separate light switch were in the same box. When I opened the box and pulled the switches out to start the swap, I was shocked to find the box jammed full of wires. I thought to myself this isn't right, what the heck is going on here. My 15 minute job came to a screeching halt while I figured out the rats nest of wires. For reasons beyond me, I found pigtails, connected to pigtails. After labeling the wires and removing everything, I rewired it back the way it should have been, minus several unnecessary wires.
