Republicans today talk about nothing but Reagan 24/7. When was the last time you heard one of them say anything about Nixon? They have completely disowned him because he resigned in disgrace.
At the time, yes these were transformative elections, but today they are (mostly) forgotten. The '68 Dem Convention is remembered for various reasons (The riots, the Daley/Ribicoff fight, the Vidal/Buckley fight, etc.) but the actual election results were pretty boring aside from George Wallace.
I don’t think it is just because of Watergate.
It is likely because Nixon was considered a political disappointment by the Movement Conservatives. He didn’t lower any taxes, he continued the Great Society programs of LBJ, presided over bussing and affirmative action programs and failed to “win” in Vietnam.
The only reason for why they stuck by him in 1972 was because they were terrified by the Democrats.