American airports are inefficient. Unless you're flying from a rural airport, expect long security lines. Even with TSA precheck it can take 30 minutes. I also recently found out it is not always open (only during core hours).

Also we don't have good mass transportation. If you're in EU, Asia you can take a train and be pretty certain you'll get there on time (barring a big event). In the US...a crash on the interstate can wreck your day. A sporting event can cause huge traffic jams on the main arterial road. So I to leave my house early enough for the 2/3 hour "before the flight" to pad for that.

My recent international flights were out of Mexico, London, Hong Kong and security lines are short. I was expecting some kind of secondary check point (Having said that I recall flying out of Toronto and it was like Disney world line)