Without contemplating the many other factors, the rhythm of a top 200m and a top 400m can be different for the same athlete.
Not in every case, Michael Johnson, Marita Koch look to be exceptions. But for many people the action in a 400m is based around economy and if you do enough work in that rhythm it can be difficult to change up for a great 200m in the same season.
That may be a deficiency in the athlete/coach/program. Obviously it would be nice to run PBs for every distance, every season, however it often doesn’t pan out that way…