He's a Birmingham fan.
Also, I think people underestimate the combined impact of money and a non-dysfunctional setup. United have been gazumped previously due to the former under SAF - mainly by Chelsea and Romanbucks - and then as a result of the latter (through combination of executive and 'footballing' incoherence or inefficiency) post SAF. In light of a takeover and ETH in place, the power Klopp's previous achievements held aren't just fading as active counter-currency but his very longevity (and the more general tendency, which he exhibited at Dortmund, for managers to lose their efficacy at a club after a certain period) has to count against them. Madrid essentially have their longterm midfield 3 in place and aren't going to pay 120+ for a first-reserve.
United also have a track record of concrete interest in him, and the negative factors that were at play at the time (lack of coaching pedigree from OGS; tarnished brand and recent reputation for exec mismanagement. JBs own uncertainty about starting given expecttaions of the club, even in their then precarious relationship to challenging for top4/trophies, and his age) have more or less dissipated.
It would still help to have confirmation of Glazers out ASAP and time to work on the deal (which, whoever buys him, probably won't be completed before early Summer, if this year)