If aliens really invade the earth, what is the reason?

I think if aliens invade the earth, they may not be able to stay because of where they live.

There are many American TV shows that aliens invaded the earth because they wanted to occupy the whole universe, but I don't think this is realistic, let alone whether aliens are really so magical. They have to pay a high price to bring the army to the earth, and they should not feel so stupid. So I don't think they will take the initiative to invade the earth, but will be passive.

If aliens passively invade the earth, it may be because they have to do so. For example, the planet they live on can't meet their basic needs. Just as we humans are now thinking about what planet we can find to live in in case there is no energy. I think if there are aliens, they may also be considering this problem. Then, if we happen to find that the earth is habitable, and we are afraid that we humans will not accept them, we may choose to invade the earth.