Can't say I blame them. UPS would totally use/abuse that as their driveway all day long to no useful benefit of anyone or any road's traffic. Their current access point to 28, 38, 93, 99 via Washington is perfectly adequate; they don't need to be gift-wrapped any lazy shortcuts. And there's not going to be as much other traffic-generating biz left on the 3rd/Innerbelt block when the GLX yard razes the MS Walker and DPS plants.
Community Path ped connection primarily serves the Cambridge side. Any of the office workers there in the landlocked south Innerbelt are going to be spending their money in Cambridge or Boston for lunch when that opens.
This is still your "pedestrian access" to East Somerville and Sullivan, and that's not going to change too fundamentally with the Community Path angled away from East Somerville and the Sullivan environs. So of course Somerville is going to prefer a thru road it can justify lobbying for a bus route on. It's the only way those remaining 30 acres landlocked on all 4 sides by tracks have possibility of becoming fungible redevelopment to them. All their Innerbelt redev action is north of the Lowell Line embankment where it's well-connected to (their) civilization.
There really isn't a high- value proposition thing they can do with those remaining 9 non-MBTA buildings on the 3rd Ave. block except the same light trucking it currently serves. This is like the Widett Circle no man's land of the northside. Planners may try to brainstorm because--
land!...big rectangular parcels!...my instincts compel me to force-fit mixed-use somethingorother because reasons! But at the end of the day it is what it is: an inaccessible bowl surrounded by a moat of noisy train tracks and a really shitty draw for mixed-use developers' money. For the same reason Menino's overtures to devs to build on the Readville moonscape fetched zero interest from any of the usual big money suspects.
You can't not have some modicum of trucking business in town like a local UPS warehouse any less than you can't forgo train yards and successfully supply your spiffy new billion-dollar rapid transit line. It's kind of necessary economic activity and land use. This is the place those things can do their necessary thing for a functioning society with the fewest people noticing it's there. Nothing wrong with that. North half of the Innerbelt's still got plenty of redev juice to tap.