Why is the tongue the strongest muscle?

Your tongue on the other hand can apply different amounts of force in multiple applications.

However all of this is a myth as the tongue is not the strongest muscle in the body. The masseter is.

It really isn't. It depends on how you measure strength. Technically, the strongest muscle in the human body is the masseter, or jaw muscle. However, much of the masseter's strength comes from the jaw's leverlike power.
The quadriceps and gluteus maximus are strongest in terms of striated muscle fiber density. And if you measure strength as endurance, one tireless muscle obviously beats the tongue- the heart.