ASL is a beautiful language, but doesn't mean it's easy.
Hearing parents have little incentive to learn ASL if they have a child with a CI. If the child is implanted early, the child can learn speech almost just as well as he or she can learn ASL. This way, the parents don't have to take classes and have individual instructions like my parents did. (Note: my parents are immigrants, so it was doubly hard for them to learn a third language on top of English.)
Plus, at this point, a child with a CI still needs speech therapy. That takes time ane effort. To add ASL instruction to the to-do list of a busy family? I don't think so.
Many experts advocate an oral-only method of teaching deaf children with CIs. I'm a living example that it can be done differently. I learned speech while I used an ASL interpreter at school. I, however, understand why the experts advocate this method. You need to compartmentalize the two languages. Nobody should sign and speak at the same time if they want to master either language. ASL has a different syntax than English, so you wouldn't get much benefit. (This is my opinion, not an expert opinion.)
On a personal note. Once I got my CI, my family basically stopped learning ASL. My sister can only fingerspell. My dad can barely sign anything anymore. My mom knows a good amount, but it's nowhere near fluency. My point is that people will take the path of least resistance. Dual language acquisition is a path of many obstacles.
Not only is ASL acquisition a logistical nightmare, it's a cultural obstacle. Every parent wants to share a culture with their children. Having the child participate in the Deaf community can feel like cultural abandonment to many hearing parents (consciously or subconsciously). You are no longer the primary cultural influence in your child's life; the Deaf community is.
ASL anchors the entire Deaf community.
Without ASL, there is no Deaf community. We band together not because of our "hearing loss" but because of a common language.
Like English, Bengali, French, ASL informs the cultural underpinnings of the Deaf community. Deaf history shows the importance of ASL to Deaf people. It's not something we'll give up easily and gladly.
In the 1800s and early 1900s, many educators tried to eradicate ASL in favor of oralism. They wanted to assimilate deaf people into the "mainstream" community. Many deaf people suffered because of this. They received marginal education because they couldn't understand the spoken language. One of the older deaf men that I knew in my childhood couldn't get a job better than a janitor because he received no valuable education from his oral school They just tried to teach him how to talk, to no avail.
Amidst all of this, a vibrant community emerged. People would converge at Deaf schools and churches just for a chance to use their own language with someone else. A feeling of kinship grew in face of oppression. (Yes, trying to abolish a language and forcibly integrate people is oppression.)
Many Deaf people throughout history fought very hard for the right to sign and live on their own terms. One example is the Gallaudet protests of the 1980s. The thought that this hard-earned culture will disappear because parents don't want to learn ASL sparks abject fear and anger in many Deaf people.
And why not? Wouldn't you be angry if someone told you that your culture is outdated and irrelevant now?
Deaf parents are like hearing parents. They want to pass on their culture to their children. Not child abuse, I think.
The Deaf Community serves as a vibrant, engaging culture that provides a safe space for Deaf people.
Whenever I meet a Deaf person, we spend a good chunk of time just talking. Regardless of socioeconomic class, race, ethnicity or region background, we find kinship. Because of my Deafness, I have friends from all over the world, all kinds of backgrounds.
How many cultures can say that?
I'm fully prepared to be one of the last few people who can walk into both worlds--hearing or deaf--but it grieves me. The Deaf culture has shaped me for the better, not for the worse. I just hope it doesn't disappear in my lifetime.
Why does it grieve me? When all is said and done, the hearing world still sees me as somewhat defective. The Deaf community doesn't.
In the Deaf culture, unlike the hearing world, I'm just as good as everyone else. I'm a true equal. I can't say that about the hearing world. Most hearing people see me as "missing something" and feel sorry for me. Pity is the last thing I want. Deaf culture doesn't pity people like me, it values people like me.
Unfortunately, that'll disappear someday because of technology. Just remember, at this point, a CI cannot replace natural hearing. Until then, deaf children with CIs will still be at a disadvantage, but they may not have a Deaf culture to fall back on if they want.
Perhaps the eradiction of Deafness as we know it will benefit society, but it saddens me to think that people like me will never exist in the future. Ah well.
Just for everyone's edification, I would teach my deaf children ASL and give them a CI. The world is a harsh one for the disabled, but I'd want to pass on a bit of my own language.
Addendum: I don't intend this answer to encourage or discourage parents to implant their child. I believe strongly that it is the parents' decision (hopefully well-informed). That, of course, goes both ways. That's the price of individual freedom; people will do things that we disagree with. C'est la vie.
The original question and discussion can be read on Quora here