If they were right, they didn't have the conviction not to give up.
Possibly not so much not having the conviction, but disillusion with human nature, no real direction and starting families. There were many factors, I suppose.
Many of the communes started with high hopes and idealism soon fell into the usual splits between a few who saw fit that they should lead and those who didn't have the knowledge or experience on how a commune/community could run. Many became disillusioned and drifted away into "normal society".
Groups which were formed to bring in more equality and social reform lost their direction or turned violent, such as the SDS.
There was Woodstock, which was the epitome of the period, and then there was the Rolling Stone's concert at Altamont Speedway which became a 'death-knell' to the aura of the Hippies.
I think, and this is my personal opinion, that we came to see a prevalence in human nature as it was, and still is, being based on greed, selfishness, material lust and 'every-man-for-himself'. The dream just disintegrated.
But there were those who were Hippies who retained the principles we sought during that period, even though we sank into the morass of commonality over the years. Eventually, the principles became more important than the life we built inside the rules and walls of whatever society we were in, and we broke away.
Some discarded everything and went completely off the grid. Some tried to inject their principles into the society they were in by holistic businesses and the like, or by getting into politics.
But you can't break or change any system when you are in the midst of it. You only become an island in a sea of slime. An exception which proves the rules.
Maybe the principles will become more alive and prominent again. Who knows.
Yes, many of us were Idealists and we wanted to change the world.
Many of us still do.
But not by violence. Not by changing the system. Probably in some other way which may become apparent in the future.
So, many of us just wait and hold our principles close to us.