Not able to get crank bolt into bottom bracket spindle
The picture of the left side of your bottom bracket without the bolt is not real clear, but I wonder if there's a round obstruction partially blocking the opening and preventing the threads of bolt and BB from engaging. Normally there is a mm or 2 of unthreaded counter-sink at the beginning of the spindle's hole prior to the threads beginning.  While it could be a photographic anomoly, I could see some of that counter-sink--or some threads themselves--galling and upon removal of the original bolt, get spun up at the opening, creating a partial blockage. That would cause the symptom you describe.

At any rate, here's example of a replacement bottom bracket (not a recommendation).   You'll need to select the correct length of spindle, but as you see, they're relatively inexpensive and replacement is appropriate regardless of the reason the bolt won't engage.