I was watching some top runs and noticed they go back to the hotland bridge a few times, what's the reason for it?

Most of the glitches in the game are performed using the Punch Card. Every time you use the punch card to skip a mettaton cutscene (cooking show, news show, opera cutscene), the game still thinks you're in the cutscene and doesn't let you use your menu (so you can't use the punch card). Going from the water cooler room to the bridge room gives you your ability to use your menu back, so the runners will do that after every skip that takes away their menu.

another thing to note is after the opera cutscene skip, your story flag isn't set correctly so when you go to the bridge, you won't be able to return back to R3, so make sure you go to the bridge between MTT resort and CORE first to update your flag, and then you can go back to the bridge to get your menu back.