Rates for new installations are much lower. Complicated to work it out, but seem to be around 4p/kwh. Also, the landlord would not benefit from any feed in tariff as the tenant pays the electric bill and would receive any feed in tariff benefit.
I rented a house in the UK which had solar panels but we never received any money from the electricity generated with it(I knew that's the deal going in, but still).
Uhm.....back when? In the UK out of the 9 houses I rented so far 8 were 80+ years old, and the last one was "only" 40 years old. Installation of solar panels on houses this old also presents some challenges, as most of them will have original roofs quickly approaching a full century. And if you need to replace the roof just to install some solar panels it quickly becomes an unprofitable idea.
Who cares? Statistically most houses in most places don't have solar. No amount of justification or argument will go back in time and retroactively change that historical fact.