You do realize that there are requirements (capacity, lighting, etc) laid out by the WPIAL that have to be met in order to host these games right? And interested districts submit a bid to be considered? The WPIAL has to pay to rent the venue, they don't just show up one Friday and play. So yeah, you have no clue how any of this works.
This is because the WPIAL is run by PSAC gym teachers. There's no national HS football requirement that they meet certain guidelines. They came up with them themselves at the bar. If they insist on playing the 5A and 6A finals at a HS, they could very easily schedule that game 7 days prior in Allegheny County. Of course, they'd need a list of schools ahead of time willing to accept their rent money. For example, it was widely known since August that it was going to be CC vs NA. They could have asked NH if they wanted to host if its those teams. NH wouldn't have turned down the revenue.