Some users might argue with what I'm about to say, but the biggest weakness has to be the manner in which most users view it as a store of value... The vast majority of people [especially in the past few years] prefer to hodl it, as opposed to actually using it!
There are two reasons that I can think of for which I wouldn't blame the majority of people holding their bitcoins instead of using them. The first one is of course a lack of opportunities for them to use their Bitcoin. What does an average person do with money? They buy groceries, pay their bills, and do other similar things with the money they earn, and if such an ordinary person buys some Bitcoin, they wouldn't think of using it for all these things mainly because they don't have places for it.
I know that if someone tries, they might find a way to do all these things using Bitcoin, maybe by finding third-party services, etc., but that wouldn't be convenient.
The second reason is that it generates money. If you buy $100 worth of Bitcoin when it's priced at $20k, your $100 turns into $200 when it reaches $40k, and people can see that happening, so they are doing what others are doing, and who doesn't want to earn money?