You can't really upscale a digital video that was originally recorded at a lower resolution. (However, some films recorded on analog film stock had a much greater resolution than what could be reproduced on home media at the time, which is how some TV shows and movies can be remastered and released in modern day HD or 4k formats. They simply go back to the original film stock and digitize it using modern technology)
Back in the early days of youtube, the technology was much different. Affordable video technology was barely beyond VHS, and was just starting to enter the miniDV era with SD resolution. Most people had flip phones *without* even a still photo camera.
Technology has leaped forward quite a bit in the past 15-20 years.
Back around 2004, Sony released the *first* consumer HD camera, which was almost $4,000 at the time. That would be about $5,200 in 2020 dollars.
Today, you can get a cheap tablet or smart phone for under $200 with at least one built-in HD camera. Frankly, that's amazing.