yet people are complaining that it has been a bad investment
I think that is because in the long run, people tends to be used in the fast changing price of Bitcoin and that is not dumping but they are used to pumping. Since the price are changing fast, they always think that it will always be a pump and they are scared of the dump. They are complaining since they are scared of what may happen in their investment.
Actually, it is true, me too I was scared of putting my money in crypto especially if I feel like its a large amount. So I always make it a point to put only money I can consider lost.