Some possible reasons to use scotches instead of handbrakes (off the top of my head) in a freight yard:
(1) I have seen photos of older wagons with brakes so badly maintained (slack adjuster rusted solid and blocks worn) that even with the handbrake wound hard on, the blocks were an inch from the wheels. Bear in mind that the FOC operating the wagons may not be the owner, ECM or maintainer of them......
(2) Some continental practice is not to use (or have) handbrakes. So, if you have a yard which receives traffic from the continent, you may be better off having a "scotch not handbrake" rule so that you don't get caught out.
(3) DB are German-owned, so the continental culture may be an influence
(4) On some types of wagon it can be difficult to see if the brakes are on/off and if a handbrake is hard on and cannot be budged (without putting air through then exhausting it) then more chance of a handbrake being left on, whereas the long-handled scotches are much easier to (a) see and (b) consistently remove.
I don't work Toton so I don't know which of those (if any) reasons is relevant to them. But there are some sound reasons why a yard may have a "scotches vice handbrakes" rule.
TPO