It's an old game and its predecessors used even more verbs.
To understand why they had all those verbs, you have to understand where it came from. Before LucasArts (née LucasFilms) started making Adventure games, Sierra was the driving force in the industry. In Sierra's adventure games, movement was done with the mouse, but all other interactions had to be typed.
Maniac Mansion, LucasFilm's first adventure game, started with a list of 15 verbs they thought were the most commonly used in adventure games.
It's important to note that Maniac Mansion didn't have auto-highlighting when you moved your mouse over something. "What Is" was used for this. "New Kid" was used to switch between the 3 characters on your team.
Either Indiana Jones and the Last Crusade or Secret of Monkey Island also introduced the concept of a default action when you right-click. Right-click will seldom actually solve a puzzle even if what you need to do is the "obvious" action.
These verbs changed slightly over LucasArts first few games (except Loom) until you got the original Secret of Monkey Island interface.
You'll notice that Read, Unlock, and Fix were merged into Use, while What is was replaced with Look at when auto-highlighting was added.
However, LucasArts realized that more of these verbs were extraneous and pared it down even further in their next game, LeChuck's Revenge: Monkey Island 2.
Turn On and Turn Off got merged into Use, while Walk to just lost its place entirely. Instead, you just click on something that's not an item and you walk there. At this point, LucasArts also changed the inventory from being a list of item names to having graphics for the items.
This was used in all subsequent games including the CD version of Secret of Monkey Island (pictured in the question), up until Sam and Max: Hit the Road.
Sam and Max was the first LucasArts game to remove the actions from the screen UI, giving the game designers more space to actually have the playable part of the game. LucasArts remaining SCUMM games did this is various ways:
- Sam and Max had the cursor change depending on the current action. Right-click switches actions instead of being the default action. Items are accessed by clicking on the box.
- The Dig had no actions, items are accessed by moving your mouse near the bottom of the screen.
- Full Throttle and Curse of Monkey Island used a 3-item Verb Coin that only appeared when you held the left mouse button down. Items are accessed by pressing the Tab key.
(All above images are from Wikipedia)