clearstream
(He, Him)
The RAW mandates that the DM might call for a check. It's DMs judgement. In the DMG there is guidance for the DM. Normally, walking across an empty room doesn't need a check. Normally...The passage you quote also explicitly states it's part of the play loop, and even mentions the "chance of failure" and "uncertain outcome". I will ask you yet again: who determines if the outcome is uncertain, when it's an NPC acting on a PC?
The 'middle path' advice encourages a DM to sometimes decide something automatically succeeds, or is an impossibility. It's up to the DM.
It's possible that a great deal of how a good DM ought to rule is being conflated with how per RAW a DM must rule...