Youtube videos have very high storage and bandwidth issues. Indeed, it is amazing they were able to even realize it in the earlier days. Make or break initially for the product was in solving the technical issues, so focus must have been on making it work acceptably. In early days, the videos were low resolution with low frame rates. The app might need to determine each user's bandwidth on the fly and adjust so the videos aren't excessively glitchy or have long pauses for downloading.