Brian Mitchell of all people offered an interesting theory. (Laugh if you will, he doesn't know anything about baseball and so on ...)
It isn't so much that Scherzer is trying to stretch his limits; he's trying to determine his limit. He pitched into the seventh in order to determine if, at this stage of the season, he can go seven effectively. I think he found out maybe he can't. Sure, he can go nine innings occasionally and seven or eight often, but not necessarily this late into the season. Don't forget, he was nails for six innings in game five and was pulled in the seventh after a homerun.