It's not necessarily about competition, it's about visibility. If I create something and I want to share it with people, that means I want people to see it. It doesn't necessarily mean "I want people to see this more than other posts", just "I'd rather not be posting into the void".

For instance, I make YouTube Shorts for a game I play. I don't post them on Lemmy anymore, because the Lemmy community for the game only has 60 subscribers, most of whom aren't even active accounts anymore. The highest-upvoted thread in the community has 47 votes, the second-highest only has 9. This translates to effectively nobody on Lemmy seeing the videos I made, because this small, slow-paced community's posts get drowned out by everything else.