It’s possible. The DSLAM/RT only has so big a pipe. If you’re out in the boonies - far from the CO - then you’re most likely on a RT (Remote Terminal) which has limited bandwith back to the CO (Central Office). The situation is not nearly as bad if you’re close to the CO where you would be on a DSLAM (Digital Subscriber Line Access Multiplexer).
Not like cable, which is a totally shared “pipe”; (A)DSL is a point-to-point line (from you to the switching office).
I was going to say something about the switch/router at the main office not being able to handle the load allotted by the telco, but zoid did it better than I could’ve hoped.
Yes, but the contention in ADSL occurs beyond the exchange. The OP should Google “ADSL contention”. Typical contention rates are 50 (50 people sharing the same bandwidth), maybe 20 for business users. To avoid being vulnerable to one bandwidth hog spoiling it for everybody, they divide the bandwidth into pipes, so that the hog can only clog up one pipe. But at peak times these days, yes the total bandwidth does become insufficient.
In case you ever wondered why “serious” business internet access is so expensive although the specs seem modest compared to consumer plans - issues like this are the reason.