One of the major reason why bitcoin could last this long is because it is not under any regulation, it is decentralized and controlled by nobody hence its volatility and ability to sustain to this moment with it value and price appreciating so high every day. Bitcoin inception ushered a new financial system void of irregularities and even wealth distribution. However, is volatile nature makes it a good investment option as many would be able to take profit from it when they invest into the market. Bitcoin is a good symbol of digital currency and so far, it has gained traction all over the world with increasing adoption.
Bitcoin is decentralized but do you really think that's the reason why the price is this grown? Have you check Blackrock wallet and some other prominents wallets of some institutional investor's? If they move their coins an inch from their wallet addresses to any centralized exchanges, trust me the market will complete the parabolic without wasting time.
Bitcoin is also volatile in nature but it doesn't display it madness like the altcoins because having more diamonds hands that are strong minded investors unlike the altcoins that people do play with around anytime and the existence of teams around altcoins kills it growth, most often makes useless decisions that affect the growth of the project.