The graph is scaled per inhabitant, which means that eg. India's apparent minor bump is actually massive. Here's the Delhi Metro, which has gone from 0 to 350 km in 20 years:
The graph doesn't account for population growth. Which is why India's growth is not looking great, but in reality, India has built almost 900 km (560 miles) of metro rail in the last 20 years, making it the third largest metro rail system in the world. (After US and China) They have additional 779 km (484 miles) under construction, which on completion will put them ahead of the US.
https://www.youtube.com/watch?v=WjG0quY5uoI
And the rest of the country is following:
https://themetrorailguy.com/metro-rail-projects-in-india/