They are in A-pillars on most cars I think, as part of the overhead curtain airbag system. (They are on both of mine, anyway; I don’t have a full dataset.)

There will usually (maybe it's mandated?) be a little symbol on the pillar, like this one: https://imgur.com/20lNA99

My truck has big labels letting you know there are airbags in the A-pillar.

Speculation: total car mass implies the need of increased structural support in the case of a roll. I'm also guessing it's regulated

If it's not airbags, it's crash test ratings. The death machine must only be a death machine to people on the wrong side of the line in the venn diagram depicting the set of owner and family.

Any vehicle I have ever owned has them in the A-pillar. Not sure how they would work in the B-pillar with the seatbelt and all, but I am no auto expert.