I think a lot of airlines/operators have just followed on from an old tradition of turning your landing lights on when you enter "indian terrritory" which was always considered anything below 1000ft, as in the good old days of daks, cherokees, chieftans, etc most of them could not get above that alt.
With fast moving jets entering that area, it made sense to turn on the lights, to help with those a/c looking for you.
I know down here in Cape Town, we have a SRA below our TMA and it is a requirement to have your landing lights turned on, not that anyone complies with that!!!!!