Why are some digital channels on VHF?

[Kevin Vahey]

I am curious why in some markets some stations have been assigned
digital channels in the VHF band? For example WBBM-DT Chicago is now
on Channel 3 and will move to Channel 12 next year.

In New York  WPIX-DT is on Channel 12

LA is all UHF, as is Philadelphia, Boston,

These seem to be the exception to the rule but there must be a reason for it.