I wonder why the doctors offices set up appointments if they are just going to let people without…

I wonder why the doctors offices set up appointments if they are just going to let people without appointment go in front of you. l been at this office for 30 minutes so far and l have an appointment and they end up telling me " we have a lot of new patients coming in and we are behind". I'm really ready to just walk out. I'm hungry and tired ( l came here after work). 😢