Why would massive insect die offs have catastrophic consequences?

It's sort of like in the ocean. Because of overfishing by all nations on earth in the oceans, we have massive jellyfish blooms because there are no fish left to eat them. Then, the jellyfish put out their tendrils and kill whatever little baby fish are left so they don't grow up. It's kind of like that only on land.

On land, insects are eaten by birds who are then eaten by predators like cats, and predatory birds and on up the food chain to the top. Without enough insects many birds cannot eat enough to survive so they die in larger and larger numbers changing the ecosystem in various ways on up the food chain.

All these things in the oceans and on land drastically change the lives of everyone in various ways. For example, if there are not enough flies, carrion can lead to much more diseases in humans around the world because there aren't enough flies in the form of maggots to eat all the dead things on the surface of the earth and this will greatly magnify many different diseases that would be controlled with more flies worldwide.

There are infinite changes taking place on earth right now like this that will change everything in really drastic ways over time both on land and in the seas worldwide from now on.