Historically, the outer Fitchburg saw 90 minute headways during midday. Perhaps the current hourly headway is seeing incredibly low demand, so they are experimenting with the 2 hour headway, which, to be fair, is the only option if you are going to keep the inner section of the line on today's (much better) hourly clockfacing frequencies.
As for Foxboro, it's an interesting question. The problem with the current Foxboro route is that it bypasses Walpole, which is still well within the "middle tier" of demand that Norwood sits in; Foxboro is farther away and in the wrong direction so it's unlikely for Walpole commuters to use it as an alternative. If memory serves, anecdotal evidence suggested that the original pilot resulted in major overcrowding at the Norwood parking lots.
Perhaps there's some level of "use it or lose it" politics here, so the T is opting for the midday service to "hold" the line until a rebuild at Walpole can allow both Franklin and Foxboro trains to stop?
