"all zone 1a to zone 1 have cheaper options" which in many cases are also waaaayyyy slower and less reliable. from my experience T buses get delayed much more often and by much longer than the commuter rail. some examples:

newtonville to boston landing: 6 minutes vs 50-60 minutes with a transfer

belmont to porter: 6 minutes vs ~30 minutes with a transfer

waverley to north station: 23 minutes vs 1 hour with two transfers

wedgmere to west medford: 3 minutes vs 40 minutes including a transfer and a half mile walk

unless your zone 1 stop is on a frequent bus route or a "rapid" transit route, looking at current estimates it is anywhere from ~3 to ~15 times slower to get from zone 1 to 1A without using the commuter rail. not to mention transfers (likely outdoors and standing) and needing to walk.