Umm...you should be happy.
It's a good thing .. i'd be concerned if it wasn't moving alot. Enjoy them Movements it's The one thing I missed the most after having my first 2 kids .
Because they are alive. Do you wake up in the morning and stay catatonic for long periods of time? I highly doubt it. Babies move just like every other life with a heartbeat (kittens, puppies, tigers, etc.). Growing, stretching out, rolling over, all of these things are practice for outside the womb
The baby moves because it has arms and legs and the baby moves around a lot because it's growing and bones are developing..