I fell in love with ASL as a child. I sat in classes with my mother at 11 & 12 then continued in college courses from age 16 until I graduated college.
I didn't learn ASL in order to teach ASL. I doubt that anyone does. We learn it and then love it.
I teach it because I want to teach children and families. They can't just go to the local college or high school and take a class.
I teach because when I see a grandma able to communicate with her adopted grandson, I feel like I am making a difference.
I work with kids because I was a kid who wanted to learn and there were no classes. I earned a M.Ed. with my studies in Deaf education but life hasn't allowed me to work in a school full time. I use my skills to help other hearing kids get that taste of ASL that hooks them. If we don't hook them, where will be get interpreters? All CODA (children of Deaf Adults) do not want to interpret.
I have taught in a private high school and have seen those kids grow and go on to be active in the Deaf community.
Also, the benefits to learning a second language are not limited to communication. Learning about other cultures and languages helps us to open our minds to other worldviews and other people. Teaching ASL not only teaches a language but helps the students to be more open-minded and accepting or others who are not like them.