Why is there always mostly skinny people in workout videos?

Working out does change your body.The people who work out in videos earn money that way.Some are fitness trainers and their body is used to thinning out and they replace any fat with muscle because their bodies need it.Their bodies are like advertisement.A person can use their videos and acheive some level of fitness like them.Its very possible to get a body like a fitness trainer if you train and put work in it, so its realistic.They are thin because they work a lot to keep their bodies toned(some of them, specifically fitness trainers who make fitness videos)
There are some bigger people who do workout in some videos Ive seen, but they are more so just a bit more heavier, not by much.