Quite naturally - 1960s were the time when we discovered that Solar System is a pretty barren place. Mariner IV sent back pictures of craters on Mars - proving it couldn't have an atmosphere dense enough for people. Venera series probes proved at about same time that Venus surface was unsurvivable for anything we could recognise as "life". Stars are too far away. That was about it.

Many people don't get the origins of enthusiasm of first years of the space era, it wasn't because of politics, it was because there were real hope to find intelligent life in the Solar System itself - as crazy as it might sound now. And almost total surety of finding at least some form of complex, multicellular life. Disappointment when the real data came in, was massive. That's why space program went nowhere after Apollo, becoming a politicised clown show - by the time Apollo 11 landed, it was abundantly clear there wasn't much to see or do in the Solar System.

It was because there were real hope to find intelligent life in the Solar System itself - as crazy as it might sound now.

Yes. Von Braun wrote an otherwise realistic novel in which earth's explorers find intelligent life on Mars.[1] Heinlein wrote realistically of native intelligent life on Mars and Venus, with far more benign environments then they actually have. But once probes got there, we got to see how bleak they are.

There's a little hope for extrasolar planets, now that we can detect some of them.

[1] https://en.wikipedia.org/wiki/Project_Mars:_A_Technical_Tale

In 1965, Clarke, Asimov, and other science writers were at NASA watching the first images appear. "Craters. Duh, it's right next to the asteroid belt, of course it has craters. Not that any of us thought of it beforehand..."

Yup. One early Arthur C Clarke story had plants growing natively on the Moon.