Why do they always only have one massive entrance to each enclosure? Why is it large enough for the Dinosaur to walk out of? Why don't they have two doors in series, airlock style?

Wasn't the issue with Indominus rex that the dinosaur tricked them into thinking it was gone and they left the door open, like idiots? Definitely some things in those movies are engineering issues, but it mostly was a problem because there were multiple points of failure in the system. This is the point I make about my work. My department catches behavior problems from reports, discussions, interviews, and providing technical assistance. We do tons of work regularly and there are overlapping ways to catch the same problem. When my department is given more work and no new staff, they can't stay on top of everything. They still catch things because the work they are able to do usual catches one of the multiple opportunities. With enough workload added on eventually you end up missing something. When the stakes are life and death, you have multiple layers of protection programmed into the system.