More and more people have to work with video files and movies. This is because of their job, or for their own ads or commercial products, or, which is more often because people want to edit their vacation or birthday videos on their own. There is no practical use in hiring other people for editing personal videos because almost every user can learn how to manage such simple tasks. However, if it is possible to learn editing videos for personal use, it means that videos for a job or commercial projects can also be managed without hiring third-party professionals.
Modern equipment like cameras and even smartphones provide decent quality, and developers find it better to issue editing software online as well. So little surprise most more or less advanced users start looking online for programs to manage their files.