Why marketers fixate on it
AutoMod rules often say some version of 'account older than N days and more than N comment karma'. If you are under the line, your comment never reaches a human. Farming karma in unrelated meme subs sometimes fails the 'karma must be earned in this community' variant. Read the specific rule.
Chasing karma as a goal produces comments nobody needed. Earn it by answering. The warm-up guide is the pace that gets you over a typical gate without looking like a farm. If a sub says karma must come from that sub, comments in r/aww do not count, no matter how many points they have.