Okay Stack, I got it. It's because the path from LA to London follows exactley along the path of a polar jet stream. This increases the planes speed and presumably makes up for the longer distance. Theres no significant jet stream if you went in a straight line on my map. See the attached flight path and stream path. I mapped them out on my original more accurate map too.
From your jetstream image below, seems like there's one that follows mostly my straight line on your map, it's the most southern one. Why don't they use the majority of that one instead of going way north out of their way to catch the most northern jetstream?
Admittedly, this flight path is also a straight line and the most direct path on a round 3D earth map from LA to London (see attachment). So, I guess It's what you want to believe.
Here's a fun story on how a jet steam pushed an aircraft past 800mph. https://www.thetravel.com/jet-stream-propels-record-breaking-l-a-to-london-flight-to-801-mph/amp/
Yes, on a globe earth it's referred to as a great circle route. It's about 5500 miles. If I were to transpose the blue straight line flight path I drew on your map on to a google map, it's about 12,000 miles.
So here's the conundrum: On your map, the arced flight path you have is way longer than the straight line path I drew, which is way shorter. (average flight speed from LAX to Heathrow is around 500 mph. But yes, sometimes there are anomalous super highspeed jet streams, but those are the exception)
Airliners could still take advantage of a jetstream for most of the journey along my blue straight line path. On your map, planes should be flying over South America and a portion of Africa because it's way shorter and there is a jetstream to support most of the route.
The fact of the matter is that your map has planes going way north out of their way which, belief or no belief, doesn't make sense.