Not social media driven. People did it for the Queen Mother in 2002, and also for the Queen's father in the early 1950s. Arguably, fewer people are going now than then, given the much wider media coverage. Back then, people were much more likely to want/need to see it for themselves.
My mum wanted to go as a mark of respect. Her desire to go is most definitely nothing to do with social media. Thankfully she decided that amount of time on her feet was beyond her, but had it happened a couple of years ago, she would definitely have gone.