Worth noting that the Democratic wave of 1974 (which hasn’t been replicated in scope by either party since) came only two years before Ford nearly won re-election, and only six years before Reagan’s new realigning coalition came along.
In 1974, 43 House incumbents retired, which was one of the highest numbers in decades (1952 had 40 retirements) After 1974, the number of retirements kept increasing for both the House and the Senate:
House:
1974-43
1976-47
1978-49
1980-34
Senate:
1974-7
1976-8
1978-10
1980-5
Basically throngs of old school New Deal era politicians of both parties started retiring (plus the ones that were defeated). This slowly hollowed out both parties in preparation for the coming realignment.
When Boomers took over Congress in the Republican Revolution of 1994, you see the same pattern in the amount of retirements:
House:
1990-27
1992-68
1994-48
1996-49
Senate:
1990-4
1992-9
1994-9
1996-13
The amount of House retirements since 1996 has never gone above 40 (at least according to the data going up till 2012)