1. USB-C is more technically complicated, especially when you want to create a host, and especially when you want to do anything faster than USB 2 speeds. Fully-integrated chips for USB-C are still quite rare, so you have to hook up a handful of different not-exactly-cheap chips to add a USB-C port. On the other hand, USB-A is pretty trivial and can be added at basically zero cost.
2. There's still a wide USB-A ecosystem out there. Having to use adapters suuuucks, so people want to have at least some USB-A ports in their system. Moreover, a lot of more-trivial peripherals feature USB-C ports rather than pigtails, so you can easily connect them to USB-A ports with A-to-C cables.
The balance will slowly shift towards USB-C, but it's not exactly surprising that USB-A is still quite common.