I grew up near Milton Keynes and am pretty sure that was the first gig for about 20 people in my school year.
In retrospect it's kinda something they never tried to book another show like it over there. Looking at their tour history between 2008 and the loss of Chester, there were 3 UK arena tours and a headline slot apiece at Download & Sonisphere. Feel like if they got the crowd to come to Milton Keynes - a venue I'm aware Londoners love to whine about having to trek too - they could've booked a big London stadium show. But maybe they didn't realise they could've done it at the time. I dunno.
I wonder if the fact rock as a whole had a bad 2010s where it just seemed to slip back in the public consciousness didn't help. In 2009, there still seemed to be quite a healthy rock mainstream but the backlash to landfill indie just seemed to count against it.
Certainly I can't think of many rock bands who broke through in the 2010s at festival headline level. 1975 are the obvious ones, maybe also Bastille, but the numbers are nothing compared to the avalanche in the late 90s/2000s.