probably just preference, I just like to target a muscle group per day. I feel I get better results too and am able to do more exercises. for example, I only see one back workout in that whole routine other than pull-ups/chin-ups and deadlift. no hang cleans, flys, etc. so when I workout I'll hit chest one day, then hit back, then shoulders, etc and this way I can workout everyday without a full day of rest because my big muscle groups are getting rest every other day. but I can still take a rest day if I want, but my muscles never feel spent which might happen with push/pull in my experience (however I do more exercises than that routine).

idk, if you've been doing it for a while and like how you feel I'm not gonna try to persuade you to switch it probably just comes down to how you feel and if that routine helps you reach your goals then it's solid for you.