Well, it seems that most fashion fans also have this idea. As I skim different fashion blogs and street style outlets for looks I want to write about for outfit lab, the H&Ms and Forever 21s start to become less and less as the blogger becomes more well known, more successful and starts to receive gifts. However Zara usually stays strong. The three bloggers above blog from London/Paris, LA/San Francisco and Barcelona respectively, so it's definitely not a regional trend, and when street style stars are photographed outside shows, a good amount of Zara makes it in amongst the designers that prevail.
The sophisticated structure, thoughtfully placed colors and grown up patterns that still manage to be fashion forward, not to mention relatively successful and abundant runway copies (or close enough) make Zara a go-to for all items from basics to outerwear as well accessories. Zara works as a stand alone, even their plain items speak for themselves and are bold enough to carry an outfit, but the basic nature and good construction of each item also makes them ideal for layering and manipulating and styling as each person desires.
This common thread that runs internationally really speaks volumes about the brand, and it helps explain why when I walk into any Zara store I have to aggressively talk myself out of purchases in order to maintain a balance in my bank account.