Your own posts explain why they didn't – building anticipation.
Look at all the people on this forum who are wetting their pants with excitement over any hint of new information. Why would Canon waste the opportunity to build even more interest over the coming month or so? By the time this thing gets announced, they will have enough pre-sales on Day One to outlast supply well into 2021. And, don't forget, the early adopters premium is pure profit for Canon and its retail partners. Given what a disastrous year this has been, they need to squeeze every bit of profit out of the market that they can and it's the affluent enthusiasts that the R5 appeals to who still have disposable income to spend.