If it were guaranteed that the price of bitcoin would stay the same as it is today, would you still buy it? My guess is, the answer is no. But if its value lies in being a currency, price stability is essential. And if your answer is no, how is it then not just a Ponzi scheme? In other words, everyone is buying it on the hope of someone paying more for it in the future, not to use it as a currency.
Your statements are incomplete. You say in title about value and then you say about the price.
If the value would stay the same most smart people would invest in Bitcoin. Because fiat decreases in value over time, including the Dollar, so Bitcoin would mean the best means for safe keeping.
Even with keeping the price and not the value would mean a good place to hide money, to store money for the kids, to transfer big amounts of money fast and cheap, to avoid embargo and so on. So... many have reasons to buy Bitcoin as long as it doesn't fall.
You need some imagination, but Bitcoin is way more useful than just a speculative vehicle to hope to get rich.