The folks at Slate wrote an article on why babies need more tummy time. In short, they're missing milestones because they are placed on their backs to sleep and mothers don't put them on their tummies at all.
There are plenty of comments about evolution, chemicals in bedding made in china, how nature made us co-sleepers so we wouldn't facilitate dingoes eating babies, "This article is spot on!", "This article is crap!", "Doctors are idiots!", "Mothers are idiots!"
Pretty much exactly what you would expect.
I'm still waiting for someone to say what I always say...
Why don't you take him out of the automatic baby swing with the spinning toys hanging eight inches in front of his face, put him on the floor, back or tummy, whichever makes him happier (I have a guess!) for a few minutes at a time, and see if he doesn't start trying to check off the boxes on your milestone chart?