A lot of people wondered at the time why that button exists - I think the answer is something like "it is only pressed by competent and trained professionals after they have followed a number of protocols to make absolutely sure there is nothing on the single line" (at this point I can hear safety and human factors experts crying out in pain). Maybe that protocol involves scratching your head and wondering if you can remember recently signalling or accepting a train in the other direction!
There was a time when, whatever buttons or levers you had, nothing goes on the single line until someone has found the token. You wonder whether a digital "TOKEN OUT" light would be possible on the signallers panel.
Driving at caution is great when you're looking out for a possible broken rail, tree on the line, or a huge maintenance trolley left behind by an incompetent overnight repair team (this happened not too far back), or when you're expecting a train ahead stopped or going in the same direction.
In the German case, you have a train going from A to B correctly going at linespeed under greens, so even if you signal the train from B to A into the section at caution, you're going to have a bad day. Perhaps lower impact velocity/energy, but I still wouldn't fancy the probability of survival under those circumstances.
Switzerland does caution if you're instructed to pass a red light, I think Austria does too?