Why are there 4 water heaters in here?

This home inspection today I found 4 water heaters installed in a 1,900 sqft home. This is very excessive.

Originally there were 2 heaters, 1 for the master suite and 1 for the rest of the house. Those storage tank heaters went bad so they installed 2 new tankless heaters. Due to the size and trouble taking out the old heaters, they still remain in the attic. They were emptied of water so ore leaking won't occur.