They're still successful in their domestic setting, which is a huge part of what fans desire, and have in recent years reached two European finals along the way.Why would anyone feel sorry for them? Selling players just results in someone from the youth system stepping up, and puts better players in the youth system because their parents / agents know its an almost guaranteed way of getting playing time and a big move at the end of it. Meanwhile they get stuffed with cash.
As business models go its light years ahead of anything in the Premier League.
There has been peaks and troughs and you would expect with more to come, but as a fan base I don't think they will be too unhappy with their business model.
Well, bar failure to get a European title after reaching said finals., but even then it's a lot more than most teams have experienced.