Some airports are gate restricted, like LGA and STL plus many others, go read the on line game rules that gives you this info, plus there is a max number in others that you are allowed
What online rules are there other than the wiki? I have read it, read the FAQ, no mention of gate restrictions.
I can live with it, although it alters my strategy. I saw Woody sweep in and buy 35 gates and I can't buy 3? So I build a terminal.