How did Facebook Messenger decrease to a quarter with the latest update?

There is more than one way to do the same in software, and not every way takes up the same size (not at the same speed). We can compare this to the following: either the right and the slower and more difficult path can be chosen to reach the left ear with the right hand, reaching out from the bottom and fast and easy. The result of both is the same, and the decisive factor is the way of going. When you use the easier way of writing a program, it takes up less memory because less code is written. The size reduction in the application you mentioned (Facebook Messenger) is probably due to this reason. They have found a shorter way of doing the same.