A few thoughts come to mind on this.

With strippers and some stitch and glue designs a plumb (or nearly so) end gives a square end to work from. With a stripper it means you don't need to taper each strip at the end. With a S&G it gives some substantial wood to glue to. As an alternate, consider a bpw that came to a point. All the S&G panels would taper to narrow pieces that would hardly have room for the holes for the ties that hold them together.

You get a bit more volume in the bow, allowing the bow to rise over waves. the added volume can increase cargo capacity, too.

Some people believe that the hull speed increases with the length of the waterline. With a plumb stem you get a slightly longer waterline. I'm not convinced the difference is noticable. With a pointed stem the effective waterline is shorter, and the hull reacts as if it had greater rocker. It turns in place easier, and can be more difficult to keep in a straight line.

Probably a few more design reasons which others will mention.

hope this helps

PGJ