You didn't enter your starting charge as 100% I think. I only show a stop at Pembroke Pines for this trip and arriving at 15% charge to KW. Obviously if I put a desired arrival charge it would be different, but since I don't really know what charge the OP would like to arrive at I'm leaving it out.
I imagine that the only time most navigation apps will plot you to stop at Marathon would be on the way OUT from KW. Inbound you can easily make it from other Superchargers all the way down to the Southernmost Point in KW. As long as you plan on charging at your destination at least. Especially since the speed limit on US-1 through the keys is rarely above 60 as I recall.