Why downloaded videos by VidMate can only be played using PLAYit?

I have downloaded a video from YouTube using VidMate. The video is in 1080p and is in MP4 format. > When I tried to play it on mobile, it was not playing. I also tried it on PC using VLC Player, but it can't play the video too. Instead, the player shows this > I tried converting it, but no video converter is able to convert it. I researched VidMate and found out that it says "use PLAYit player to play the video". When I download the app, it plays successfully. Why can downloaded videos by VidMate only be played using PLAYit even though it is in MP4 format?