With all this water in the basement, there isn't any room for storage. What a waste of space.
With most of the water gone, the dampness remains. This leads to that musty smell.
Most houses have a weak sump pump in the basement. What good is the sump pump in the middle of the floor if the water is coming in through the walls?
A lot of basement have appliances such as water heaters, clothes washers & dryers, or HVAC units. If these things get wet and ruined, you could be looking at thousands of dollars to replace them.
Even after the water drys up a bit, the residue is left behind, along with the smells and stains.
This home in Lincoln, DE had water throughout the basement. It almost rose up to the bottom of the elevated water heater. It was impossible to store things, making it a lot of wasted space.