The universe is expanding, that doesn't mean items within it grow, they just distance themselves from eachother and that we do observe.

Imagine a balloon you put some marbles into while it's completely deflated. Now inflate the balloon. Marbles stay the same size but the space between them increases.

The speed at which the universe is expanding is not locally sufficient to overcome the gravity (and other forces) keeping the Earth together.

There is a very strong force holding the Earth, the sun, and the moon together known as gravity, which prevents them from separating on their own. The universe's expansion is unnoticed from our own galaxy. It's really on much larger scales, between galaxies, where the universe's expansion is noticeable.

Metric expansion is incredibly weak over distances smaller than galaxy clusters, so you just don't see any local changes. Gravity can easily overwhelm metric expansion, although if metric expansion continues to accelerate indefinitely, you end up with a "Big Rip" scenario.

For small scale objects (where "small-scale" means like planets), gravity is enough to hold matter together and keep it the same size .The expansion of space is extremely minute and weak at distances as small as planets. It's distant outer empty space that is expanding, space that is empty on a size scale billions of times bigger than planets.

Because the universe expanding is a bit different in this case.

Imagine you have marbles and you drop then on the floor. Every little bit of time you move them a bit outwards from each other. That is essentially what the universe is doing when expanding.

Imagine you are standing in one spot wearing roller skates. On your left is a 250 lb NFL lineman. On your right is a 50 lb child. They each begin pulling on you in opposite directions. Which way will you go?

The universal expansion is like the 50 lb child, gravity is like the 250 lb lineman. At distances smaller than galactic clusters, gravity wins.