The main reason, ironically, is because it can not be regulated. This puts it in direct conflict with every government, who all desire control over their own currency. This guarantees that Bitcoin will only ever be used for things which can only happen outside a regulated banking system. It is also not particularly good at criminal transactions, since it is more transparent than a bank account. Here in Germany crypto is essentially illegal. Of course you can buy it, but transactions require you to deanonymize.
Another reason is of course that it has become an object of intense speculation, which creates high volatility. This drastically decreases it's usefulness as a currency, since holding Bitcoin is a major risk.
Can quantum computers factor arbitrary numbers with 4 digits already?
How are you right? do you believe in yourself enough to put your money at it? If not, this conversation makes no sense.
A significant amount of bitcoins are held by known entities (exchanges) so it's pretty trivial for institutions to keep their coins after a fork. Those of you self-hosting might have some losses.