One reason is that the way swimmers approach a season is totally different from the way runners approach a season. Swimmers only rest (and shave) for one or two meets per year. Chances are slim that you see any particularly fast times coming out until the designated peak meet of the season. At that peak meet everyone is interested in swimming fast times and just going for it because its one of the few times that they actually can. Swim racing is much less about tactics than it is about just going and hammering the entire race. This was probably the first race Peaty felt decent in since 2015.
When I first started running I found it bizarre that runners would post PRs midseason and then championship races would often be a tactical affair. Over time it grew on me - if you get catch a cold a few days before your only peak meet in swimming for the season it kind of makes all the work across the season feel like a waste of time, especially when its a 20+ hour per week commitment at the NCAA level. Even if you don't have the race you were aiming for at your peak event in track, maybe you ran a PR or had some strong races earlier in the year so you can at least feel like you accomplished something over the course of the year.