I think people are just getting better. 1K and 1100s of today are significantly better than they were a year ago.
I also think that “smurfs” are sometimes just players who had a bad streak or are trying new strategies.
Last time I came back to play, I ended up trying a new civilization and ended up dropping from mid-1K to low 900s before climbing to 1100.
I wasn’t smurfing, but it took a few losses to figure out the new civ/ strategy.
On top of that, I had some weird crashes that dropped me down a bit further.
I really think people are mostly just getting better.