I would have said the site had an upload limit size ... which is governed by a setting in something called the IIS. However it is possible that it is something having to do with your connection with the internet. You could try uploading a file to another video service (if not youtube - vimeo or something similar) to see where the constraint is. If you want to reduce the size of the video, you don't need to edit it but can reduce it by slightly reducing the size of the video. Consider that humans can hear between 20 hz and 20,000 hz but sound exists lower and higher than what humans can hear. Some sound compression techniques just eliminate areas that humans cannot hear. Same thing applies to images and video. Hear is a link that should reduce the size without changing the quality substantially.
https://www.movavi.com/support/how-to/reducesize.html
I have never used this so cannot speak of its quality. Alternative software is available. When you do get it up there, send me a message ... I would be happy to view and upvote.