Share to iBooks not an option!

Can anyone explain the inner workings of iOS share? Different apps get different share options.

I noticed that when I use an app with a built in web browser or when using Chrome and I come across a PDF that I want to save to iBooks for better viewing I don’t get the option of Save PDF to iBooks. Even if choose edit they aren’t share options.

If I copy the URL and paste it into Safari I get the option to Save to iBooks and Save to Kindle.

Any idea on why the share options would be restricted? Anyone able to explain why there is two rows: color and b/w for share?

Just trying to make sense of it all.