Because Steemit is not like any other platform. It's easy to upload a photo (that many time is not yours) to Facebook or other social media platform, sit back and wait for likes. That might give people satisfaction. It's easy to collect meaningless upvotes using other people work, it's harder here on Steemit.
You can't do that on Steemit. Here you need to work hard to get somewhere and you also need to learn. There is a financial part that needs good management, and let's not forget that engagement is key here. If you want to succeed, you need to work hard.
People tent to choose the easy way. Why go take photos when you can take someone else's photo? Why work hard to write and article when you can just say a few words and post a selfie?
And let's not forget the fact that Steemit is not ready for mass adoption yet, it's still in Beta form.