There's a good technical reason for keyboards and mice to still be USB A: adapters from USB A socket to USB C plug are allowed by the standard, but adapters from USB C socket to USB A plug are forbidden (because they would, together with a common USB C cable, allow creating the forbidden USB A to USB A cable). This means that USB A keyboards and mice can be used in both USB A ports and (with a simple passive adapter) USB C ports, while USB C keyboards and mice could be used only on USB C ports.
Therefore, until having enough free USB C ports in computers is common enough, using USB A ports (with an optional adapter to USB C on the box) on the keyboard or mouse makes sense. This is similar to how, during the transition from serial and PS/2 mice to USB mice, it was common for them to come with a adapter which allowed them to be used either on a USB port or (with the adapter) on a PS/2 port.