So, I'm guessing this was more a joke than a question, but the Blue Line basically pre-dates the airport by 19 years. The East Boston tunnel was opened in 1904 and ran from Maverick to what is (basically) now Government Center with stops at what is now Aquarium and State.

The 1954 extension to Wonderland used the Boston, Revere Beach and Lynn Railroad right of way to get to Wonderland. Hence, the airport station is where it is. It wasn't really placed there so much as that was where they could get the train to go.

Back in 1954, air travel wasn't that common like it is today. Check out the airport in the 1920s: https://www.digitalcommonwealth.org/search/commonwealth:cn69mx627, https://www.digitalcommonwealth.org/search/commonwealth:cn69mz00f, https://www.digitalcommonwealth.org/search/commonwealth:cn69mx962, https://www.digitalcommonwealth.org/search/commonwealth:cn69mx848, https://www.digitalcommonwealth.org/search/commonwealth:8k71nz49t. Even in 1936, it looks like basically nothing: https://www.digitalcommonwealth.org/search/commonwealth:cn69mx741. Even in this image circa 1955-1964, it's still pretty primitive looking: https://repository.library.northeastern.edu/files/neu:m0472z357. It's definitely starting to take shape, but doesn't seem like that big a deal.

Ultimately, a lot of our train lines run along rights of way that already exist and it can be difficult to get new ones. Plus, diverting the train to the airport itself likely would have required quite a tight turn and the 1950s were starting to be the era when rich people wanted to use their cars. Boston was spared some of the auto-supremacy thanks to governors Volpe and Sargent, the latter who cancelled many of the highways that would have cut through Boston including the Inner Belt (which would have run through Union, Inman, Central, Cambridgeport, BU, North Brookline, and Melnea Cass Blvd), the Northwest Expressway (which would have run through Arlington, North Cambridge, Porter, and Union), and the Southwest Expressway (which is where the Orange Line is today).

Yes, it's disappointing that the Blue Line isn't closer to the airport, but given the time it was built and the right of way that existed, it seems less ridiculous. And as bad as it is, most American cities basically don't have public transit...though how I'd love something like DCA where the stop is right at the terminal. At least we were spared three additional highways cutting our city apart?