When did lightning delays become a thing? Like when did they institute the rule about the 8 mile radius, 30 minute delay?
Sorry late to the party and didn't read from page 2 on to see if your question was answered.
This has always been a thing, but never really enforced by Stadiums and racetracks.
In August 2012 a fan was killed and 9 were injured at a NASCAR race in Pocono. In 2014 there was a lawsuit against Nascar and Pocono. In 2016 the courts ruled in favor of Nascar and Pocono, but it was a huge fight.
Now I can't find any story that organizations like Nascar, NFL, NCAA, MLB etc took that as a warning, but it seems as though these last 3-5 years you have seen much stricter enforcement of lightning policies because nobody wants to be put in that situation.
Again this may not be the definitive answer, but connecting the dots it seems to point to this incident as a change.