Why are other planets unfit for human habitation? Explain why.

First of all, no one says that other planets are not suitable for human habitation, but that there is no environment suitable for human habitation on the planet currently explored.

Most of the explored planets have no liquid water.

There is no suitable atmospheric environment, or there is not enough oxygen in the atmosphere for human to breathe.

Many known planets have great temperature difference between day and night, which is mainly due to the improper distance between these planets and the stars in their galaxies.

Gravity. The gravity of some planets is too great or too small for human survival.

At present, the speed of interstellar travel owned by human beings is too slow to realize fast interstellar travel. It takes too long to travel from one earth to other planets, and it is impossible for human beings to migrate on a large scale.

With the rapid development of science and technology, human beings can find a planet suitable for human habitation in space sooner or later. Human migration is an inevitable trend in the future.