Irrespective of doping - which has always been around and as much of a suspicion when the previous record was set - it's probably a combination of factors:
- Spikes - they're destroying the longer distance records that the times are almost irrelevant. For instance I'd say Bekele's 12.37 or Gebrselessie's 12.39 from 20-25 years ago, is worth more than Cheptegui's 12.31 in trampoline spikes and wave-light pacing. The unknown though is how much of an impact they are having on the sprints. Nothing in the men's 100/200 suggests they're having a big impact, although the women's times are exceptionally fast, but it's interesting that both 400m hurdles events' records have gone recently and perhaps there's an additional advantage in the hurdles.
- Track - tends to generate more marginal improvements over time, as opposed to the step change we're seeing with the spikes. I think the super-hard tracks of the 1990s at Toyko and Atlanta in particular really pushed times on in comparison to previous eras, but nowadays every major championship has a fast track so the difference is not as jumpy, but more marginal and gradual
- Competition - it's the longest standing men's track record so has been overdue for getting broken and it's more about having the right talent jostling to break it. If we track recent performances, Warholm has been peppering the record for some time now, suggesting he's capable of 46.5/6 on a good day. Same for Benjamin really. Moses clocked 47.02 in 1980, so the fact it had only gone to 46.78 in the 40 years since suggests it was ripe for a bigger improvement. It's a bit like Pietro Mennea's 200m record of 19.72 that stood from the 1970s until Johnson smashed it with 19.32, and Fredericks also clocked 19.6 in the same race. Or Bannister's sub-4-minute mile and within a year a bunch had gone under. When a record is a bit soft, it's not uncommon for it to be destroyed.
