MySQL 5.7 statistics - Change db
You are probably using a 3rd party package.  And it probably does a "USE" at the beginning of every connection, possibly much more often.

The frequency of SHOW commands also smells like a sloppy 3rd package that can't remember what it is working with.

Another possibility is a monitoring package.  However, I would expect to see even more SHOWs.

One way to track things down is to turn on the "general log" for a short while, then look at that log to see which "user" is doing what.