system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why are the vid players on some "big" sites so unreliable?

It's gotten to the point where I hesitate to click on any vid not from youtube, simply because the user experience for other sites is so iffy. Vice videos seem to take forever to load on both my (admittedly ancient) laptop and my snazzy new iPhone. CNN, Twitter, ESPN all range from unreliable/slow loading to occasionally actually crashing my computer. Watching videos on Vimeo is absolutely torturous, which is unfortunate because they have a lot of good, exclusive content. These are companies that are focused on video and have a decent amount of funding. What is youtube doing differently that these companies aren't able to do?
gpt
YouTube processes every single video that is uploaded to the site to use the exact same file type with the exact same settings. This particular file type is heavily compressed. Compressing the video file causes a loss of quality but it loads faster. Vimeo uses a slightly less compressed file type which looks better but might take longer to load if you have a slow internet connection.

The other things that can affect your viewing experience is the physical location where the video is stored, how many people are trying to access it at once and how capable they are of accommodating the traffic. YouTube has spent a ton of money placing data centers all over the world with enormous bandwidth to accommodate the incredibly high site traffic that they have. So going to YouTube might be like traveling a mile on a six lane highway, and going to CNN might be like going a hundred miles on a winding back country single lane dirt road.