Most doors that are controlled for handicap accessability are control using a hydraulic cylinder that costs hundreds of dollars, and not a motor. Any motorized doors cost way way more than that.

I had the same thought when I was younger about putting generators attached to a bouy in the ocean, which has waves constantly and would generate power all day. Just like your door idea, it would work and would make power, but it wouldnt turn a profit. Its too expensive for the output you would get in return. So… yeah… we are gonna continue to burn fossil fuels for now cause its the cheapest… once we deplete enough of them that it gets more expensive than something else, we will switch to that until we destroy the world, or skynet takes over and we become the next power source.