I think perhaps you are casting to precisely where the bottom of the CharacterController’s shape is, judging by line 23 above.
This would mean the CC is keeping you from casting.
Try making doing 0.1 or 0.2 MORE distance than half of the height the way you are now.
EDIT: I’m no longer convinced the above is correct; but make some gizmos as RadRed suggests. 
Just so you know, the CC can be used for groundcheck.
I wrote about this before: the Unity example code in the API no longer jumps reliably.
I reported it to Unity via their docs feedback in October 2020. Apparently it is still broken:
Here is a work-around:
I recommend you also go to that same documentation page and ALSO report that the code is broken.
When you report it, you are welcome to link the above workaround. One day the docs might get fixed.
If you would prefer something more full-featured here is a super-basic starter prototype FPS based on Character Controller (BasicFPCC):
That one has run, walk, jump, slide, crouch… it’s crazy-nutty!!