We are talking a UK-specific relaxation.
The UK visa situation was unique.

The country is a major generator of trips to India: yet despite the contribution promised to India's travel and tourism industries the government insisted on maintaing what were in effect stringent restrictions on UK passport holders, while lifting restrictions on other nationalities.

I have no idea what quid pro quo Modi was waiting for, or if he got it. But he was certainly under pressure from the Indian tourism sector, and from the UK government. Maybe the new UK prime minister was uniquely placed to exert specifically focussed pressure: who knows?