Try flying out of SFO when there’s a sprinkle of rain or fog - 1/2 hour delays and/or 30+ minute ground holds at departure airports. And, that’s in the early morning. By the afternoon, it’s into the 2+ hours sometimes. Any airline would still gladly sell you a 40 minute connection at SFO in July or December even though there’s a 70% chance you’re not gonna make that connection. If you must make a connection, allow for 2+ hours plain and simple.