Why do some parents refuse to teach their native language?

My parents were immigrant children long ago (both were 5 year-olds), father from El Salvador and mother from Mexico.

Yet, only English was spoken at home. They refused to teach me Spanish. I started practicing it on my own a couple years ago. I'm still not very fluent but have been improving.

Why do some parents refuse to teach their native language?
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By refusing I feel they made me lost part of my heritage. I could've communicated more with the hispanic community.
Here I am: clearly latina in appearances, Spanish last name but not fluent in the Spanish. I'm catching up though.
Why do some parents refuse to teach their native language?
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