It's simple: "Diesel forever", and making sure the finger is on the scale for that being the only achievable end result.
They don't want to do any BEB's beyond what they feel they absolutely must hold their nose and do (namely: Silver Line). They want the TT-to-BEB replacement to fail so hard it gets them out of needing to buy any more BEB's for anywhere else in the system. How else would you have them do something as ass-backwards as requiring deadhead charging runs to tiny North Cambridge instead of putting up charging spots around Bennett Alley and Cambridge Common right outside the Harvard busways. Or Watertown Carhouse and Waverley loop. If you could charge at Harvard/Watertown/Waverley, there'd be enough range to cover all of the 71/73's schedule blocks instead of "maybe if we cross our fingers in 2024 they'll make a vehicle we can get on the property by 2026 that'll do it." If you could charge at Harvard/Watertown/Waverley, there'd be enough slack capacity left at North Cambridge to BEB the 75 (since the 72 now appears to be permanently defunct) and possibly also 77, instead of all of that tiny yard's capacity being wasted on 25% spare ratios for the 71/73 and load relief being a decade away because of Charlestown being scheduled last in the garage renovation pile. As is, we're getting outright service reductions with the 72 giving up the ghost...even though they *claim* that they'll be ordering somethingorother with left-handed doors for Harvard and won't be harming accessibility in the process (until then, Sunday boarding practice every day is going to be the open-ended "solution"...very overtly harming daily accessibility).
They're hustling every piece on the board to make those 35 BEB's they haven't yet ordered be such born failures that they become the *only* first-gen BEB's the agency ever attempts to order outside the ones they have no choice but to employ for the Silver Line. They want the deck stacked so arbitrarily against them that we never reach a point in the next 2-4 years where their feasibility for the routes becomes even a ballpark possibility, so they don't need to place the order at all. Or, failing that, the pilot units fail so hard upon trial that they can be returned to sender as quickly as possible. It's imperative to them that the technology fail SO spectacularly hard that it leaves a crater they never have to clean up, and that there's no pressure to revisit that unpleasantness for another 20 years and 2-3 gens' worth of battery tech...saving them the indignity of having to plan internally for anything different than Yellow Line ops autopilot.
The inconvenience of having infrastructure set up for quick-charging extended-range ETB's was so troublesome to this goal that it needed to be nuked from orbit at lightning speed and massive tactical coordination. Hence, the over-the-top ratfucking of the cities over road construction, the sandbagged cost projections for maintaining the wire, the lies that the current infrastructure doesn't even permit the icky in-wire charging. They so don't want BEB's anywhere in yellow paint that it was treated like a grave existential threat to be exterminated. It's bigger than a hate-boner for trolleybuses...they don't want electric bus tech ANYWHERE on the system, and are willing to move heaven and earth to poison the well ahead of it. It's several degrees beyond mere regressiveness.
