I am guessing (and agreeing) with Ton.
If the Tools panel doesn't fit in a single column, it goes to a double column so you can see all of the tools. What I have seen in various classrooms is that the monitor size and resolution has an effect, as does the size of the Illustrator window (it should be maximized if you are close to the "breaking point"). There is a fine point where I think it fits on some computers and Illustrator disagrees. Illustrator wins—always! Other times I am willing to live without the bottom tools until I need them, and I put it in single column until I need those tools.
Two solutions I can think of since this is your own setup and not a classroom situation:
- Get a bigger monitor
- Create and use a custom toolbar instead of the default toolbar
Show another screenshot of the Toolbar when you have the Essential workspace and it's been reset and the you have changed your Toolbar to single column.