A bit like the stock exchange?
No, that was my whole point, how did you not get that? If at some future date the world is run by solar-powered robots and capitalism as we know it is obsolete, if someone could add up all the money put in and all the money taken out of shares, the money taken out will be many, many multiples of what was put in. Because the money put in earned profits. While some people may lose money in shares, there is no fundamental theoretical reason why every person who ever invested couldn't have got more out than they put in. The same is not true of bitcoin.
TBH I'm just repeating what I said in my original post, if you didn't get it the first time, this probably isn't going to help. I don't know how to make it any simpler.
(But, yes, bitcoin is like currency, if not shares. Currency trading is, in aggregate, not a way of making money either. Currency, whether held or traded, traditional or crypto, is not an "investment". )