Due to the scarcity of Bitcoin, it can never be used as money or currency. Whoever has even small portion of it, prefer to hold it till it's value appreciate to a level where he has made huge profit.
Bitcoin is seen by many as store of value. New adopters are buying it because they know it's price will shoot up and they find it as good investment.
I think this is the key factor here.
Also, I mostly agree with Murad Mahmudov's Lindy Effect chart:
^take note that this was posted in 2018, so the "We are here" part might be outdated.
I am not so sure about that. No matter how big the market cap is, or how low the fees are with LN developments, I think if Bitcoin is perceived as more valuable than other currencies (fiat and shitcoins) people will tend to store it instead of keeping it. That's what Gresham's law states. But it doesn't matter what Gresham said or not. Just think about it: if I can use fiat currencies that constantly lose value of Bitcoin that it's the best at keeping it, which one am I going to use?