1. The aliens visiting earth are not intelligent creatures. They used to be intelligent creatures but they lost their intelligence over millions of years due to evolution. Their species became more and more like ants and the intelligence was selected against. They are not self aware.

2. They build spaceships instinctively, they were designed when the aliens were intelligent but now they just copy the same model.

3. The aliens coming to earth are coming are lost. They have a route they follow that goes by earth but some of them are taking wrong turns and ending up in our solar system. They are not trying to contact us.

4. They do not have faster than light travel. They just go really fast and let time dilation do the work.