So I was thinking about this recently, and it seems like no matter who the teams or coaches, the team down at the end of the first half has a major advantage in the second half.
This is because the losing team will make adjustments at halftime, and the winning team is less likely to (why change what is working?).
So losing team makes adjustments and if they work then they are in a better position. But for the winning team to respond to those adjustments they either need to make their own adjustments in game during the second half, or anticipate what adjustments the losing team will make in the second half in order to counter them, both of which are not easy.
All that to say, I think part of this is attributable to the fact that we are ending the first half of most games with a lead.