Even if this were to change, using object storage results in a lot of operational simplicity as well compared to managing a bunch of disks. You can easily and quickly scale to zero or scale up to handle bursts in traffic.
An architecture like this also makes it possible to achieve a truly active-active multi-region Kafka cluster that has real SLAs.
Engineering solutions which only exist because AWS pricing is whack are...well, certainly a choice.
I can also think of lots of cases where whatever you're running is fine to just run in a single AZ since it's not critical.