Second reason- radios in those days almost universally had a single ended class A audio power output stage and these by nature are sensitive to power supply ripple, so a choke helped a lot to smooth things out. Solid state stuff almost always has a class B push pull output stage that is nowhere near as sensitive to power supply rippple.
I thought the lack of sensitivity to PSP ripple in modern amps is because of the use of a negative feedback design. IE, the output is fed back to a negative input to be compared with the positive audio input, completely ignoring whatever the power-supply is doing.