I can honestly say I don't know how many parents you have been around, but the fact that you've even met those parents of deaf children shows they are at least somewhat involved with their Deaf children, which shows a bias in itself.
I also want to say, before I complain about them, that I do realize it is difficult for parents to learn sign, and becomes a million times harder when they've been brainwashed with this "Speech good, Sign bad" mentality. If you ask the general population if they had a deaf child if they would learn sign language, a LARGE majority say YES! But then they don't...is it possible Deaf children are just born to the hearing people who won't learn sign- I doubt it.
ALL of that said, they can learn it, and CAN use it. I am around mostly Deaf college students...theoretically these are the children who have, for the most part, had the most involved parents. These deaf people are all considered highly successful, simply by virtue of the face that they are in college. The % of parents that sign among these deaf people is much higher than the deaf community in general (surprise, surprise). But, even when they sign what does "sign" really mean?
Even in this group, many of the deaf people I've met have parents who don't sign. I've only met a few deaf people who actually have hearing parents that "sign" in some form or another. I've met parents of kids who grew up oral and now have learned sign, parents who raised their kids with the TC approach, and parents who had their children educated in an ASL environment. Some of the parents had one deaf child, some had multiple deaf children. Many of the parents are considered statistically to "sign well" and to "fluent communicate with their deaf children"
HOWEVER, just because they can sign doesn't always mean they do. Nearly all of the parents I've met signed when talking directly to their deaf child, or at least mouthed and gestured to the point their child understood. BUT, with ALL of them, the second they looked at another (hearing) person and started a conversation, or the deaf person would look away for a split second and seem to not be totally interested in the conversation, the signing stopped. It was "I'll do it if I have to" mentality. I, as a hearing friend of these deaf people, got really stuck in some weird situations. The parents would look at me, and if they knew/found out I was hearing, immediately spoke and didn't sign, in spite of me signing back to them, and in spite of their deaf child being RIGHT in front of them. I have avoided telling parents of deaf children I'm hearing because of their reaction, their tendency to speak and not sign.
I am sure there are parents of deaf children out there who don't do this, but many more who do...at that point, what do you think of the hearing parents? do they fluent communicate with their deaf child? How many parents out there really totally include their children in conversations? ... I wonder