The smaller rear triangle accomplishes a few things. First, it is the trend in aesthetics.. Gotta keep up with what is the latest and preferred styling. Second, shorter tubes mean less material, which equates to less weight. Shorter tube also equates to less cost of materials. Third, supposedly the smaller rear triangle provides more vertical compliance. Seriously doubt this is something the body can pick up on, but that is the claim by some brands.
No need to overthink it. Just ride the thing and enjoy yourself!