I just got into iS.
The very 1st try I got exectly the same message.

I'm quite embarressed as it took 5 trys to get in.

I think they are getting more strict (or my photography is getting worse??)

I could be way off base with this one but: I also think they reject some initial submissions to see how determined you are. Which to me makes good business sense.
If a person gets rejected and simply puts their tail between their legs and walks away, then they werent really that committed and not willing to try to improve.
If they keep trying and trying, then they are committed and willing to work at it.
Just thoughts.