Aldav53,
It's not set up that way, it's the only way to create a neutral with a delta configuration. The early history of commercial electrical use (AC) did not use a ground, as such, a bit later having already set up the configuration as Delta, manufacturers began making 110 volt equipment (even though this is REALLY a light explanation, no pun intended) so we began the center tap to create a stable reference point for 110 volt equipment.
Household stuff was not the first use remember, and 3phase is the economic choice of champions, households began being connected a bit later, from a distribution standpoint, you still fed the commercial with ungrounded (or at least, un-neutraled) 3 phase delta, and could tap the same transformer bank with the center tap for it's 110 volt loads.
The Wye, of star, was a later development, but it is not 120 degrees out of rotation like the delta. That can create it's own problems such as not quite as economical, nor pure on an oscilloscope, but is a great compromise and the one we are currently comfortable with.
That's also the reason you see so little being fed delta for the last 30-40 years. Delta primary is common, but delta secondary is pretty rare by comparison. Why delta primary? You don't have to have a ground with it, even though most utilities, at least in my area, utilize a grounded delta, but that is for lightning protection, not neutral creation. This also sets up it's own problems such as ground loops between primary and secondary, but again is a good compromise and one of the reasons power is so much more reliable than when I was.......er, younger.
