There are many reasons;

Mobile TV to handheld devices works better on UHF than VHF. A station's future may depend on the income from handheld receivers.
Converter Boxes and DTV receivers have omitted FM traps needed to deal with strong FM stations. FM bothers VHF more than UHF. (All analog TVs had them.)
Many companies market UHF only antennas as DTV antennas.
Many viewers made the mistake of installing UHF antennas for DTV.
Distributed transmitters work better on UHF than VHF. The FCC approval for DTS took years to get approved.
The higher power needed to improve indoor VHF reception will cause interference to other nearby co-channel VHF stations.
There was a knee jerk reaction to converter box rescanning problems.

VHF continues to work better with outdoor antennas than UHF.