Because you cannot freely say no to that. They have authority over you. Even if they promise it won't affect their opinion of you, you never know if that is actually true. So you are forced to play along.

"Are you planning to have children? You don't have to answer"

Asking a question in front of a group, bur adding a "if you're comfortable", doesn't really make the problem go away. There's always a pressure to answer, even if you say that answering is optional. It's not a horrible violation but it's still kind of weird and unnecessary in a professional context.

I promise you I mean this sincerely, and not in a memey internet insult kind of way - are you perhaps autistic?

I ask because this is exactly the type of comment one of my siblings would make, and she is on the spectrum. She wouldn't be able to understand the social dynamics at play here, whereas for other folks it's just common sense. "Optional" is not really optional in some social settings, and that's something autistic folks struggle with being aware of, much less understanding. The activity may be optional in the most pedantic sense; you won't be struck down by lightning if you decide not to participate. But there will be consequences.

All of which is another reason why this whole exercise is an awful idea, considering that the number of autistic folks in software engineering is probably a bit higher than the population baseline.

Kind of hilarious to make this suggestion while simultaneously revealing yourself to not understand nuance or commonsense.

Please, elaborate. What nuance and commonsense do you feel I'm not understanding?

After reading all the comments, I'm starting to wonder.