There are some things that need to be borne in mind about the GR20. First and foremost, it's an excellent route, and as a result, it attracts people from all over the world. Some of them have clearly bitten off more than they can chew, and others arrive with very high expectations about the level of services along the route, which clearly aren't met. Then again, you can get food and drink all the way along the route, which you couldn't when it was first established. No, you had to carry a week's worth of food to set you on your way!
The other thing about the GR20 is its essential artificiality. Many long-distance trails are created by linking 'traditional' cross-country routes together. The GR20 does include some 'traditional' routes, but most of its high-level stretches were pieced together by trial and error, literally forcing routes through the most formidable places. No-one in their right mind would have tried to get through the Cirque de la Solitude in the past, and I gather it took a team of mountaineers three visits to discover a route that was just about passable for a fit and agile walker with a good head for heights.
Given that the route is 'artificial', there weren't many 'traditional' places offering lodgings, such as existing farms or villages along the way. So, refuges had to be built, and then had to be staffed. Most of them are staffed by Corsicans, but you seldom meet any Corsicans walking the GR20. So, you have to imagine how things must look from the standpoint of the refuge guardians... People come from all over the world, carping and criticising the lack of facilities, clearly ungrateful that they're lucky to have ANY facilities at all, but they grudgingly stay for one night at a time, dump all their trash and expect someone else to clear it up, shake the dust off their feet and go home. I think if I was a refuge guardian, I'd probably last for about three days before throwing everyone out of the refuge and locking the door!
When I try and think of occasions where Corsicans have been brusque or offhand with me, I can only think of two. One is a hotel, and I guess most people know which one. The other was a bergerie, where people were sitting around eating bread and cheese and drinking wine. I asked if I could buy a small slice of cheese, and a young woman stomped off to a nearby hut and returned with a HUGE cheese, demanding that I either buy the whole thing, or nothing at all. Simple choice for me... nothing at all!
There have been other instances where I've tried to buy bread, cheese, fruit, and been rather surprised to be handed the goods without any payment demanded. I mean, I tried to offer payment, but in each case was simply shooed away with the goods. In one instance, having tried to pay for bread and cheese from an old farmer, he actually grabbed a big knife and waved me away with it. I was grateful for the bread and cheese, assumed it was being given out of kindness, unsullied by an exchange of money, but all the same I'm sure it could be misinterpreted as being rude or even violent by some people! I have heard similar stories of people being 'terrified' by Corsican 'kindness'.