Boston is such a weird airport I'm not sure it's worth bringing up except as perhaps an exception that proves the rule.
BOS has the "advantage" of serving a fairly large population while also not being big enough to be a real hub for anyone[0], while being simultaneously big enough to have service from nearly everyone.
Unlike a lot of airports smaller or serving fewer people than BOS (and some of comparable size), you can get from BOS to a whole mess of hubs.
A few select routes (BOS to SFO as noted) are incredibly well-served because of the volume of lucrative business travel between the two and the fact that a whole mess of airlines already serve both airports.
[0] No, JetBlue doesn't count. Boston is as much a hub for them as CLE[1] was for Continental. I.e. a second class hub at best.
[1] CLE by comparison only really serves Cleveland. Columbus, Dayton, Cinci, Indy, Pittsburgh and probably a few others from a similar radius BOS draws from all have decent(ish) airports. All of those have basically the same problem as CLE or are worse in some way. I've flown through or into and out of all of them.
BOS has the "advantage" of serving a fairly large population while also not being big enough to be a real hub for anyone[0], while being simultaneously big enough to have service from nearly everyone.
Unlike a lot of airports smaller or serving fewer people than BOS (and some of comparable size), you can get from BOS to a whole mess of hubs.
A few select routes (BOS to SFO as noted) are incredibly well-served because of the volume of lucrative business travel between the two and the fact that a whole mess of airlines already serve both airports.
[0] No, JetBlue doesn't count. Boston is as much a hub for them as CLE[1] was for Continental. I.e. a second class hub at best.
[1] CLE by comparison only really serves Cleveland. Columbus, Dayton, Cinci, Indy, Pittsburgh and probably a few others from a similar radius BOS draws from all have decent(ish) airports. All of those have basically the same problem as CLE or are worse in some way. I've flown through or into and out of all of them.