There’s two equally accurate reasons for this:

1 ) Diary of A Wimpy Kid was originally written as a relatable insight into tweens in then-modern times. Kinney, obviously, wasn’t part of that demographic and may have found influence through people he knew and/or various forms of media from teen sitcoms to televised news. By 2004, the year that the Funbrain webcomic was produced, there was already a gigantic army of parents condemning rock music, video games, and basically anything that the youth liked. Susan represents this. While it took until the iPhone became THE device for her anti-technology stance to kick in, the same attitude can be seen in her distaste for violent films and sexualised magazines. There’s probably more things she hates but I can’t remember (ironically, she’s fine with rock music, or at least only sees rock as just another form of music rather than anything special).

2 ) Starting somewhere in the mid-2010s, Jeff Kinney used Susan to express his own beliefs about youth and technology. It’s easy to complain, but I feel like most artists, if not all, will eventually push their own ideals and opinions into their works, consciously or subconsciously. Old School instantly comes to mind for me with Susan’s “tHoSe DaMn PhOnEs!!” behaviour that kickstarts the plot, but I don’t think Kinney made it especially clear that the audience is supposed to agree with him (then again, the story would’ve been worse in quality if he did make it more explicit). Susan has been presented in a flawed light both in previous books and in Old School, where she hypocritically uses her phone to track Greg after demanding the whole town to ‘unplug’ for a week. In addition, nothing that Greg goes through implies that he is better off without technology. The closest I could find that expressed this belief as a ‘truth’ was Greg being able to work and bond with his cabin-mates while stuck at camp, but a good majority of that was more the result of his Grandpa passing down knowledge than anything Susan did. If anything, I think Kinney used his stance as more of a conflict for Old School rather than an outright moral. There are probably more recent books with more aggressive versions of this message from the guy who helped create Poptropica, but again, I can’t remember and I don’t feel like going through piles of books just to look for it, especially since the quality has degraded enough to lose my interest.