As said 10 times already, the board (which are the Glazers) can decide to put in voting selling all shares, and then can vote for that to happen. It is what happened when Glazers took a majority control at United, then they forced the minority shareholders to sell and Glazers owned at some stage 100% of the shares and made the club private. Then later sold some shares and made it public again.
There are many advantages for the new owner to buy all the shares: a) they might believe that the club will be worth more in the future; b) they might plan on investing their own money in the club (stadium, clearing the debt) so why the other shareholders would benefit from them while being free riders; c) they might want to take the club private so they don’t need to publish the financial records every 6 months. And that is just out of the top of my head.