The Sims 4 Gallery is now tied together with your Origin ID, and any privacy settings you have enabled on Origin, will also carry over to your in gallery profile. As you can see in the photos below, Crinrict’s profile has the comments section disabled, while Lazy Game Reviews has the comments section enabled:
Both users have different privacy settings on Origin, which then determine the privacy settings of the Sims 4 gallery profile. It doesn’t matter whether you are following someone, or whether they’re following you, unless your privacy settings are set to “public” in Origin, no one will be able to comment on your profile.
To enable commenting on your Sims 4 gallery profile, open the Origin client (or go to your Profile on Origin.com) and select “Privacy Settings”. To enable commenting, “allow everyone” to view your profile page.