As a Boston-proper dweller, I think one of the best things about living here is my proximity to the airport, especially if a flight is early or late. Many business travelers feel the same, I know.
The solution I think is boosting capacity, amenities, and transit options between secondary regional airports, especially since narrowbodies are routinely making trans-Atlantic and transcon flights. ORH should capture a big chunk of the Western suburbs and central Mass, PVD grabs the deep South Shore, maybe MHT can entice some North Shore folks, and of course those in Southern NH. The PVD commuter connection is also pretty good as it stands, so it already has potential as a multimodal transit hub.
The problem there is the airlines don't really want to fly from those regional airports - unfortunately there's no money in it for them. It works prior to 9/11 and until 2005 or so, but not so much in today's aviation environment. It's more on airline willingness to see and serve a market than an airport can do to attract them.
Basically, regional air traffic growth has been concentrating at BOS, but not because of the regional airports not wanting the traffic. I'm sure the PVD and MHT airport directors primary task is grow passenger traffic any way they can, but it's been instead declining for years, and not because BOS has gotten that much easier to get to for passengers despite the Ted Williams. PVD and MHT both peaked in 2005, with 5.3M and 4.3M enplanements, and by 2022, that went down to 3.1 and 1.3M respectively - granted COVID depression, but in 2019 PVD managed 3.9M and MHT 1.7M. MHT in particular is way down since PVD still has a better local catchment, with MHT these days mostly seeing Spirit and Southwest flying from their for the lower costs compared to BOS. Over the same time period, BOS went from 27M to 36M, with an all time high of 42.5M in 2019.
A large part of this is due to the consolidation of airlines and the decline of regional flying. BOS had 409k aircraft movements in 2005. In 2019, despite moving 68% more passengers, it had 427k. That's largely due to more bigger planes, and fewer smaller ones. In an era of comparatively cheap jet fuel and wages, high frequency low cost small aircraft made a lot of sense in a world of hub and spoke flying, enabling you to go to a smaller airport and get anywhere in the world relatively quickly and cheaply. The problem is, especially after colgan 3407, regional operations are quite a bit more expensive for airlines, so it often actually costs more to fly out of MHT or PVD than BOS. Right now, there's a national pilot shortage, resulting something like 500 regional jets parked because there's nobody to fly them. If they prevail in court (trial is ongoing right now in Boston) JetBlue isn't buying Spirit for it's business model - that is expected to go away - but because it wants their planes and crews. Those regional aircraft were the bulk of flying at those regional airports, with the rise of LCCs and ULCCs blunting the fall somewhat.
The problem is it's also a Catch 22 - you see induced passenger demand when you have lots of cheaper flights to lots of places, meaning airlines introduce lots of service. MHT benefited hugely in the 90s when Southwest first launched in the Boston market out of MHT. You get amenties like new terminals when there are lots of passengers passing through to eat, shop, visit lounges etc, and especially if it's closer to home and has cheaper parking, it's an easy sell. Conversely, infrequent, expensive flights means you're more likely to drive to BOS, forget to even consider MHT or not fly at all, reducing the incentive for airlines to offer service, perpetuating the cycle. There's substantial incentives in place for incumbent airports and players, and It's why new airports like ex-mil ones like PSM (Pease AFB) or CEF (Westover) struggle to get commercial service going despite what looks like robust local catchment. ORH benefits from being owned by Massport which can hold Logan over the airlines heads.
The primary reason new airlines, especially low cost ones, choose those secondary airports was costs at BOS - but it appears that the fares and demand justify that, since even Allegiant, Spirit and Southwest, airlines famous for flying to secondary airports like Orlando Sanford and Chicago Midway, prefer growing in BOS. While Spirit and Southwest still maintain operations at MHT, allegiant at PSM - they're there for lower operating costs for cost conscious leisure travellers wanting to get to Florida, not because it's a robust market.
In short, the major carriers are flying bigger planes into bigger airports less frequently, and the smaller markets are getting beggared as the hub and spoke model that relied on small, cheap to operate and frequent regional flights to justify secondary markets is under strain. Many airports have lost service entirely in the past couple of years, and at many it's not expected to come back. How PVD and MHT are trying to get out of it is by courting ULCCs and LCCs as well as new entrants - Spirit, Breeze, Avelo, etc to bolster demand from players who can't justify BOS costs.