Maybe they know that if they connected the dots their funding would dry up.
BTW, this warm period also coincided with the Renaissance of the 12th Century in Western Europe.
I looked up one of the researchers Neil Wanker at Columbia Universitys Lamont-Doherty Earth Observatory_____ I could not find any global warming propaganda from him. Looks like he is fairly honest as far as climate research goes. He might be into pure research minus leftist political agenda