You’re not totally wrong. However consider that a cracked or broken carbon piece can be repaired (local guy had his rear fixed by Ruckus) whereas aluminum you need to hope you can find a used part once the manufacturer stops stocking them, and those pieces can be tough to come by. Carbon is pretty robust, especially MTB carbon, ive got a few nice gouges in my road frame where the chain dropped and it’s all groovy
Personally I’ve viewed the hybrid use of carbon and aluminum this way as a pure cost savings which many companies are moving away from. Trek 9.7 used to be carbon front and alum rear, 9.8 gave you carbon seatstays, 9.9 added carbon chainstays, now their carbon bikes seem to be all carbon. I know a guy who had an alum frame he used to transport on the back of his truck over a tailgate pad where the down tube developed dents from transport. I’ve smashed big rocks into my carbon frame and no issues, even after a head on crash with an e bike