a) Video files are large (much, much larger than pictures) and these videos have to be stored in "the cloud". Despite the name "cloud", it's actually real servers sitting in buildings which store "the cloud". These servers cost a lot of money to run (due to electricity costs) and as such storing video is expensive

b) Videos have to be converted and compressed. This requires a lot of processing, which again costs money.

YouTube and similar services cover the cost of this by putting advertising in the videos. They'll also show related videos at the end of the video. We do not do either of these things; no advertising, and no recommending videos of competitors at the end.