The hippie movement started off more or less as a protest movement that fissioned into different single-issue movements (environmentalism, women's rights, and other personal issues vs protesting Vietnam and changing society as a whole) as the 70's wore on.
LBJ's Great Society and Good Lord, how he escalated the Vietnam War made great tomato targets for critics right and left both wanting him to do more.
Nixon FWIW was an economic liberal dealing with both the OPEC embargo and winding down from 'Nam, but boy did he live up to being Tricky Dicky. Both wholeheartedly gave the FBI carte-blanche to investigate, harass, and arrest hippie activists as political subversives.
Without those Presidents as lightning rods for dissent, the main impetus broke up. There was a lot of tension within the movement between the "serious" political activists and the Merry Prankster/Yippie crowd even in the 60's.
By the time the 70's rolled around, SDS had birthed the Weathermen as our own homegrown leftist terrorist group. It was the style then. Every Western nation felt the need to have one.
Germany's RAF and Baader-Meinhof gangs, Japan, Italy, all had very active terrorist cells semi-quasi collaborating with the IRA and PLO, merrily bombing, hijacking, kidnapping, and so forth to make their nihilistic point against the Man. Police adapted, got brighter about counter-terrorist techniques, collaborated across borders and nailed them.
Sure Manson's "Family" didn't do the hippie image any favors, but mostly,
you could see a difference after Altamont. Nobody trusted each other (too many people finked on each other), nobody could agree to a common agenda, and there was a violent edge to things that turned folks off. So it became more and more personal vs social and global as mentioned before.
The political right didn't see the need for underground terrorism, as they wholeheartedly supported official violence- death penalty, no-knock laws, all the fun legal short-cuts for law enforcement to get those damned hippies under control.
Plus, you run into that whole adult life thing. Tuning in, dropping out and so forth are cool 18-25. By 1980, most of the Boomer cohort had hit thirty and needed to make the compromises everyone makes to make a living, raise kids, and so forth.
There's a saying in Europe, "If you're NOT a socialist under thirty you have no heart, but if you're still a socialist after thirty, you have no brain".
So, to keep the hippies alive as a social movement past 1975, you need to make it mainstream as a rite of passage for youth. It'd help if the drug laws were not as rigorously enforced. In a way, it has, but not in the explicitly political dedication to progressive politics.
Kids adopt a lot of the postures of the hippie movement w/o the meaning b/c kids are economically dependent way too long IMO so they've got nothing better to do than rebel. They want the emotional space to be themselves, yet belong.
Now there's not as much emphasis on physical conformity (men can wear long hair, women can dress in anything masculine, so that kind of outward statement isn't quite as powerful.
It's funny to see how many folks support school uniforms these days to remove the whole dimension of envying another kid's clothes or other gear.