If I had to speculate...

and what "sarcastic rant driven blowhard" doesn't like to do that?  I'd say that Maura Healey thinks her path to The Corner Office is thru a "Girl Fight Tonight" scenario in 2022 wherein it's the AG versus The Lt Governor, Karyn Polito.
If Healey can get a match up like that, ergo two women on the general election ballot, she can effectively negate the dreaded "girl factor" which posits that a certain increment of voters simply won't vote for a woman for high office and will cast ballots for the male opponent on that basis.
Well, Elizabeth Warren dealt "the girl factor" a very satisfying body blow back in 2012, but it made a robust comeback in 2014 in the Coakley/Baker matchup, so its very much a potential issue in any notional gubernatorial race.
Of course, if it was left up to me, I'd try and talk the AG out of the race entirely, the problem with her particular constitutional office is, no matter how well she executes her duties, its still a job that makes enemies.  If Maura Healey is doing the job right (and it seems like she is) then she is just creating her own personal aggrieved faction that'll happily knife her in the back come October 2022.  On the other hand, Baker's original majority in 2014, was a bare 40,000 votes in a open race, Healey may believe she can close a narrow gap like that in a sufficiently tight race that has no easy gender divide.
Because Believe Me, Maura Healey IS running for Governor, her signs were utterly ubiquitous in Menotomy yesterday, she is clearly assembling a volunteer infrastructure all over the Commonwealth and her seventy percent majority last night may well have topped the entire democratic ticket statewide.
The only other thing that conditions a Healey candidacy for Governor is Charlie "Lumpy" Baker's future plans.  I've long suspected he'd love to run for the US Senate, or he has supporters that'd love to tempt him into such a race. Lumpy's nearest opportunity is running against Ed Markey in 2020, which is smack-dap astride Baker's second term, something that might trigger the Governor's famous anxiety and caution.  Meanwhile Joan Vennochi (remember her???) is conjuring with a "Baker for President in 2020" meme, something I'd discount, Lumpy doesn't have the guts to directly Donald Trump either in the NH Primary or on an Independent ticket.
I'd go deeper into the mechanics of Warren running for President and somehow winning thus opening up another special US senate election and giving Lumpy the opportunity to appoint an interim Senator...but then this was a posting about Maura Healey's ambition...:)