I have misread hi10 as HEVC. According to the current logic, Hi10 will be available only on the device has hardware acceleration for Hi10 profile.
Do you see H.264 10bit in HW+ Codecs with harware accelerated mark?
If no, your device doesn't support it.
In some old versions, it was force attempted when it's enabled. But, it has been found that it's causing system level crash on many devices. So, now it's disabled by default on unsupported devices.