Why are several swap spaces being used at the same time, and not sequentially, according to priority?

Question

linux

Two swap spaces are allocated, the first /dev/sda6 on hdd is a separate partition, connected via fstab, priority is set to -1. The second one is created in RAM via systemd as a device /dev/zram0 with priority 32767. The swapon output shows that the kernel sees both swaps. As far as I understand, the system should first use swap with a higher priority (/dev/zram0), and only then with a lower one (/dev/sda6).
But judging by the information from swapon, the system under load uses both swaps at the same time , approximately 50/50. When the load is removed, swap both are also released approximately proportionally. Why?