The first thing the majority of people care about is what the OS will look like on their phone if they install it. There's not a single image of what will appear on my phones screen once I'm running GrapheneOS - that's a huge turnoff for the vast majority of people.
Compare that to apple.com/os/ios where the first thing your eyes rest on is a picture of a phone showing you what the OS looks like. Same deal for the features tab on android.com - they're showing you the features, not just giving you technical documentation for them.
If they do actually want to grow the userbase, there is a lot that needs to change - more than just getting bespoke deals to be supported on $1500+ small marketshare phones.
Regardless, the developers are very experienced and smart, and know that screenshots are often used to advertise a product, so I guess it's a very conscious choice.