Because people have the attention span of a goldfish and if you aren’t reminding them every 5 seconds of the features they have available they’ll forget they do in fact use them and then complain to support because they can’t spend 5 seconds on the help page.
I say this, not in defense of mozilla, but in frustration at having to deal daily with these kinds of issues. You can put giant screen-size arrows on where to go / what single “do the thing” button to press and people will still forget 5 seconds later.