Bitcoin is a decentralized which is not control by the government or any country in the world. that is why it will not be possible for someone to buy all bitcoin in the market.
By 2041 the 21 million cap on bitcoin quantity estimated to be reached . I don't think all bitcoin can be bought because I don't see any one in this world that can buy all bitcoin in the market.
Of course, there can be no such person who would not buy bitcoins at all, but there are many people who can simply buy all the rest.