Airbag for passengers in the rear – not possible?

Hello Have you ever looked for the help function, but found nothing. Why does no manufacturer offer airbags for the back seat? By this I do not mean the “Gardine” that comes down on the sides, but airbags that come from the front like on the front seats. Is that technically too complicated? Inzvischwen has already been solved a lot, why not that? I come to the idea because I have seen a crash test with triggering airbags. There the dummies got well in the back seat. e torn while the dummies landed “soft” at the front. Bye Tex