Nothing is stopping you. I've published papers and presented at academic conferences while working in industry. Both in collaboration with academics and without.
Disclosure: I was an adjunct for a semester while I was between industry jobs.
Because they aren't intended to be educational. Universities (as they are run today) are primarily grant-revenue capture organizations, secondarily research organizations (at least to the degree necessary that grant money doesn't dry up because of fraudulent spending accusations), and finally after that, a begrudged effort is made at education for optics. If they could ditch the education angle entirely, they'd send the students home tomorrow.
There are pure grad institutions, such as UCSF and Baylor College of Medicine