I have a child with AuDHD who has trouble masking consistently. That coupled with impulse control issues and an inability to regulate between the two just looks like chronic deception, lying for the sake of lying. It is exhausting for him and it never works in his favor. We spend a lot of effort coaching him to not mask and to not seek unearned attention, and its a huge challenge.
For some people, masking is just an easier, freer form of existence. It's like asking for a dressed up coke at a happy hour so your coworkers wont grill you about abstaining from alcohol. Or how people who work in callcenters seem to converge on a way of speaking that makes the interactions a little easier.
It's just that for autistic individuals, they are highly analytical about how everyday social interactions work and doing this costs them more cognitive load than you would expect.
No one masks at birth. If you want your child to stop masking, perhaps it’s helpful to investigate what caused them to learn the behavior in the first place and what could be done to make the experience of being unmasked more pleasant and less aversive for him.
Just as you say, masking takes an incredible amount of energy and is exhausting and often backfires. Why would anyone expend such exhausting amounts of energy without some extremely strong motivating factor? The alternative to not masking must be perceived as exquisitely undesirable.
I think with Autism the process of masking is just harder, and the ability to read social queues takes extreme focus to understand the general emotional state of others around them.
Because of things like this:
Coworker: "How are you doing?"
Me: "Bad."
The conversation, and the rest of my day, does not significantly improve from there.
Or, if you provide a never ending story they will see your disability for what it is and they won't ask you a second time.
That's masking.
"Not it's not, because if you practice masking, the masking becomes easy."