Difficult to see where the Glazers think they'll get a buyer at an even higher value down the road - it felt like Qatar was the last of the big Middle East "investors" to enter the Premier League, and if the Glazers are burning that bridge then I can't see who they think will have enough resources to buy the club down the line.
Particularly as the longer the Glazers remain then the more resources a new owner would have to pump-in to reverse the neglect from the Glazers, especially with so many other owners of Premier Leagues clubs investing, including whichever club the Qataris will surely turn to with United off the market.