Does this have something to do with the snowfield right below the summit? How are others avoiding that?
Some years a small snow field remains across the trail below the summit. It is usually about 50 meters across. If you continue along the direction the trail has been following, you come out on the dry maintained trail. It is usually better to do this than to climb strait up in snow or on loose gravel and big rock ledges. The first image is the top of Whitney from the Caltopo tool.
The green line follows the trail. The red circle is the section covered by snow. Sometimes even experienced hikers get confused by the snow. Caltopo also has overlays from USGS with the trail as dashed black and Mapbuilder with thin red lines for trails:
The USGS shortcut uses swithbacks near the top to limit the steepness of the route. The Mapbuilder has a dotted blue line where the Mountaineers Route final 400 may be, the lines marked "John Muir Trail" actually are, the trail marked "Mount Whitney Mountaineers Route" is the (more often fatal than the Mountaineers Route) Easy Walkoff and a jagged red line right of the snow for its switchback shortcut.
There are a lot of free convenient tools and data on the net. Some of it is crap. It is your responsibility to figure out which. The original post seems to be from someone using data from the current USGS map. Older USGS maps had the trail correctly. At least they noticed that:
"The map is not the territory."
Dale B. Dalrymple