I had the same reaction when I rebuilt my AR-LST speakers (which are pretty neutral)
Remember it was at this time that "hi fi" was at its zenith, cassette decks and eight tracks were how most people listened to music in cars
Most "hi fi" speakers of the day were pretty bass heavy, just about all amps/receivers had a "Loudness" button. and car stereos used those 6x9 speakers that had the Trunk to let the bass boom in the car.
When they did the mastering, they used a speaker that would emulate how their customers would listen to the music.
I am puzzled that with all the music of that era being remastered to take advantage of 30, 40, 50 year anniversaries opportunities to sell you the same music over and over why they don't fix that. Maybe it's because everybody is listening on boomy Dr. Dre headphones these days?