You can. But now most of your clients will burn battery because they don't have hardware VP8, VP9 or AV1 decoding (yet). IIUC these are the only video codecs supported by WebM and they have very little hardware support. Of course this problem exists for any particular codec that you chose it is either nonfree, inefficient or not universally supported.

And after that some of your clients will have terrible buffering because your video file is too large. Other clients will have a 4k TV and your file will be too small. Unless your bandwidth is very cheap you will also spend more money sending your 1080 video to phones with a 720p screen.

So yes you can. But there is a reason that every serious video service has multiple codecs, every client has a different ideal video file and by getting close to that you will provide a better experience.