Please stop messing with your shower drain! It is working just fine. When the water goes down the drain it falls into whats called a PTrap. This PTrap is shaped like a U at the bottom so it can hold water. It does this so the sewer smells don't enter the home.
If the PTrap drained after use or was installed at the wrong elevation it could drain or partially drain and you would have a nasty smell or funky odor in your home. It's good you cleaned the line and snaked it. But stop - your done!!!
A PTrap works like this.