I agree, the Glazers have built the worth of the asset from £0.8B (when they bought the club) to now around about £3.1B (according to Forbes). At least two of the Glazer 'clan' have washed their hands of the club and its only the three stalwarts who retain both a commercial and a personal interest in the club.
Who knows where professional football will finish up after Covid, but Utd's owners have other concerns; the ability to attract elite players, and their willingness to pay the asking price. The OT ground is beginning to 'creak' as a top class sporting venue, its position is vulnerable, with it being squeezed in between a railway line a on one side and a canal on the other, expansion on the present site would be costly and will not solve major access problems. Moving to another site would be even more costly and they would loose the 'theatre of dreams' title which is highly valued by fans and sponsors alike.
There are three things; the lack of willingness to invest in elite players, the need to redevelop OT from the ground up is impossible on the current site if a state of the art venue, including access and egress issue being sorted is required, and moving to another site loses the magic of the 'theatre of dreams' and threatens future income streams.
When these thing coincide, probably after the effects of Covid are clearly known, then the Glazers will sell, but who will buy?