PI4 versus FT8

Most beacons use PI4 whereas I would have expected them to use FT8. 

Does PI4 confer some advantages? Maybe better sensitivity? In my view, unless there is something about PI4 I don't know about, I would prefer beacons to use FT8 or at least have an FT8 sequence.

Just imagine if the IBP project beacons used FT8 on each band! One could leave a monitor on all day and see what comes through. 

This would be extremely valuable in the solar quiet years on the higher bands. 

I could see someone producing an IBP RX perhaps band switching to see which bands are open?