Yeah it's called good storytelling, his appearance may have changed but his mental and personality isn't going to instantly change as well. That'd be bad storytelling. That's why he's the mangaka and you are just the reader
Haha, good storytelling would be to
not have his looks and whole physique immediately change. He would have just got the powers, but would have still remained less than handsome. That would have really tried his mental fortitude, also in the way of possibly making him go through physical discipline and exercise to reform himself. Furthermore, girls wouldn't have kept falling for his new looks, left and right, but he would have needed to capture their attention through his deeds and attitude, including his dedication to reshaping himself.
If you think this is good storytelling, you need to climb out of the well and see the world.
Furthermore, trash like this always starts as web/light novels. The market for isekai is, currently, so vast that anything flies and no-effort works also get manga adaptations, even anime. Quality writing is way down on the priority list. The only thing that matters is that enough consumers will pay attention to yet another copy-pasta isekai. It doesn't take much. This is yet another series following the most blatant tropes of a bullied MC who gets instantly OP. Then he starts collecting a harem while remaining dense. Gee, we have only seen that a mere thousand times before.