Active Directory Domain Controller Login Load Balancing

We have 23 Server 2019 Domain Controllers: 3 at our Admin/Central Office location, one at each of our 19 school campuses, and one at our transportation/purchasing complex. Each campus/location has its own /14 subnet IP scheme, but they are all on the same VLAN, and there is only one AD site. From what I've been able to read, I'd expect the domain controller on each subnet to be prioritized as the login DC for workstations on that subnet, resulting in higher login totals at the more populated sites (Central Office, and 2 of the high schools), but that's not at all what I'm seeing.

Instead, about 25% of login traffic is going to the PDC Emulator at Central Office, with another 5% and 8% directed to the other two Central Office DCs. Meanwhile the other campuses are fairly evenly spread from 3-4% of the remaining logins each... with the smallest high school handling more logins than the other two, despite having 5% of the user count compared to the other two.

Anyone have an explanation for this?