They probably don't care enough about a sidebar because they don't know about it or it doesn't come to mind. How many users are going to go to a subreddit and think "I really need to go check out the sidebar!"? Most of the time it's there to try and improve the posting quality. If using a mobile app is a user's primary method of viewing reddit, how would the sidebar even enter their minds?
The sidebar being reachable from the context menu is nowhere near sufficient, and since this is now an official reddit app, they should care enough to promote a feature that improves the quality of reddit.
It's a cultural thing. You shame them by saying hey low content poster, you should consult the sidebar more often. Sidebar. Sidebar. Sidebar. BOOK DEPOSITORY.
And then hopefully people will get it through their skulls. The sidebar is where useful content is.
Of course this will not affect drive by users and people who have no desire to improve themselves.
One solution would be to show the 'sidebar' at the top of whichever reddit you're browsing. Of course, considering the size of some sidebars, this might necessitate a 'sidebar' targeted specifically at Alien Blue users (which is now quite feasibly, I suppose).
The sidebar being reachable from the context menu is nowhere near sufficient, and since this is now an official reddit app, they should care enough to promote a feature that improves the quality of reddit.