Why does the government try to ignore UFO sightings?

There are a few possibilities.

1. They are ignoring because they feel that it is a waste of time and money.

2. They're in fact researching but they want to keep it a secret because other countries would think that their military capabilities are limited or they just want to keep things for themselves.

3. Avoid public fear

4. US spy planes

5. Top secret developed planes or weapons.

There are lot's of reasons but at the end of the day, you won't get to know the real answer