I suspect that you can still order burgers, but to answer the OP's question, the reason why a place like Sci-Fi might get rid of that option is that burgers tend to be lower priced than most other menu items, and so by eliminating them, the restaurant might be able to increase revenues. Customers are very predictable, and so while any one of us might say, "I'll just order less and they'll decrease revenues," professionally-run restaurants, like Disney's, know when that's true and when it is false, and can maximize their profit based on their knowledge and experience.