Sure, but it’s a lot easier to make a list of accounts to follow that suggests you’re impartial or well-rounded. It’s a lot tougher to spend every day ensuring your replies and retweets do the same.
I'm a pretty big user of Twitter, including in the capacity of a journalist. But I'm highly skeptical of this reasoning. When I look at the Twitter profile of any given mainstream (e.g. ostensibly left-leaning) journalist, I'll find that I have dozens if not hundreds of mutual followers (e.g. "Followers you know"). If I look at the profile of an ostensibly right-leaning journalists (e.g. a Daily Caller reporter), the number of mutual followers is inevitably fewer [0].
I think you misestimate a few variables. For starters, journalists and most mainstream Twitter users are not inclined to doing gruntwork, such as curating a list of people to follow and then mute. Similarly, the use of Twitter lists, which also involves the manual gruntwork of curation, is very rare among the many personal accounts I follow. For 99% of everyday use (i.e. not specifically investigating someone's social media activity), journalists and mainstream users also lack the interest in analyzing a given user's followings list. Occasionally I see people mention FollowersAudit/BotOrNot. Can't remember the last time I've seen someone mention a purported political audit tool. In fact, I can't remember the last time I've seen someone mention tools like https://doesfollow.com/.
You also underestimate the perceived value of following-to-followers ratio. Almost all of the big name Twitter accounts (again, not just journalists) follow a relative handful of accounts versus followers count. It's widely perceived that a small accounts-followed number is a signal of prestige, or at least self-importance. Thus, an even lower incentive to pad that number in hopes of boosting a hard-to-perceive impartiality metric.
Anyway, the proof should be in the pudding. Are there any notable accounts that obviously stuff their followings with people they politically dislike/hate, for the purpose of pretending to be non-partisan? Shouldn't we see this in the brand accounts, like @nytimes [1], which have a desire to be seen as fair and also have no obligation/expectation to actually engage via retweet/reply?
[0] In this case, I don't think the reason is primarily caused by ideology; the number of right-leaning news outlets are far and few between, which reduces the potential of direct personal/professional ties. I find that the few former DCaller reporters who have moved to larger outlets and who I follow do not have a disparity in mutuals)
