Bowl games are fun. Certainly they don't "matter" in the same sense that the playoff games "matter"...but guess what? Those playoff games don't "matter" in the same sense that things that ACTUALLY matter within the grand scheme of life.
But, it's fun.
Also, these minor bowl games actually take on MUCH more meaning within the modern landscape of transfers and draft-eligible sit-outs. It gives a lot of young guys a chance to simultaneously play what is basically an exhibition game under big bright lights under extraordinary circumstances.
Sure, "nationally" these games don't matter one bit, but other than the NFL (and MAYBE college FB playoffs), there isn't really a "national" sporting event that everybody cares about anyway.