First reason: Bitcoin price is now clearly overvalued relative the level determined by its public acceptance rate (if 100% acceptance rate means ca one million usd, then nowadays acceptance rate is not clearly 10% but rather something around 1%).
What does "100% acceptance rate" even mean? Its a meaningless term. It would be naive to assume that everyone in world has a Bitcoin wallet. Thats never going to happen. Not everyone has a bank account - let alone the idea of 8 billion people holding their own keys of their Bitcoin wallts.
Besides, your numbers are totally made up. The claim that at "100% acceptance" Bitcoin would be worth a million dollars is speculative projection, not a fact. Its a number often used by analysts when calculating market caps, not public use. For instance, if Bitcoins market cap reached that of gold. But whos to say Bitcoin cant outperform all other assets by market cap? Bitcoin supply is a fixed and much scarcer asset, so anything is possible.