...well, that and the pandemic and the new technology.
But hear me out. Bekele set his 12:37 in 2004. He then went 12:40 in 2005, 12:48 (twice) in 2006,12:49 in 2007, and 12:50 in 2008. A bunch of other guys went fast in that era too, many in races won by Bekele. In the era before, we had Geb and Komen fighting over the event, running fast times back and forth.
Then from 2009-2017, we had exactly one race under 12:50, Paris 2012. The 6 guys under 12:50 in that race, as well as Gebremeskel's 54-second close, made it clear that 12:46 was never the limit. But it sure seemed like it. There were no world record attempts in that time period, and the main reason for this was that Mo Farah didn't want to try. I imagine he didn't think he could get there; fast, even paces were never his racing style anyway. But the reluctance of the clear fastest guy to try evidently put a damper on everyone else because there just weren't very many races that even went out at a sub-12:50 pace.
Imagine Farah had a different mentality, and had pushed as hard as he could to run as fast as he could. Maybe he even could have gotten to 12:37; I don't think so. But imagine if the 2011-2017 top-times list looked something like this:
Farah: 12:40 (2012)
Gebremeskel: 12:41 (2012)
Farah: 12:43 (2016)
Gebrhiwet: 12:44 (2016)
Kejelcha: 12:44 (2016)
Farah: 12:45 (2011)
Gebremeskel: 12:45 (2011)
Edris: 12:45 (2016)
Lagat: 12:45 (2011)
If the list looked like this (or any other ordering), then 12:37 wouldn't have looked so untouchable. Add in Brussels 2018, and we're talking a race every year or two that is 4-8 seconds away from Bekele's mark. I think there's a lot more anticipation.
As it is, Farah never went faster than 12:53 (I think he closed in 53 in that race), and he never appeared in a race where he or anyone else really even attempted to go faster than that. So we've had two races that felt like flukes: Paris 2012 and Brussels 2018. So for Cheptegei to go 12:35 doesn't feel real: it's 8 seconds faster than Barega's time that already felt a bit out there. It's 22 seconds faster than Cheptegei's old track PR, and he hadn't really been in any races that gave him the chance to go faster.
If we hadn't already seen Bekele/Geb/Komen, Cheptegei's mark would be an 8-second world record, and we'd all be super excited--like Gebrselassie in 1995. But since this was the first non-Bekele attempt on the record of any sort, it kind of feels like he sniped the record. Along with all the other weirdness right now, it doesn't feel real. 12:37 being untouchable was a constant for many years. Now the record is suddenly gone. In reality, it was never as far away as we imagined.