I think their original plan was to announce it before E3, but they changed their mind at some point. There were just too many rumors, including from Bloomberg news, in order for this to be totally nothing. The real questions are "why did they delay the announcement" and "when will it actually come"?
Some reasons why they might have delayed the announcement:
Out of these 4 reasons, only the last one suggests they are going to release the model this year. Sales are good without it? Release next year. Parts shortages? Wait until after the holidays. Key game? Well what would be the key game? The games most people commented on having good graphics were Mario+Rabbids 2 and BotW2. Both of those games are coming in 2022. On the other hand I've heard complaints about the graphics of both Pokemon BD/SP and Advance Wars Re-Boot Camp, and both of those games are coming during the 2021 holiday season. It seems to me that the Switch Pro release is going to happen next year.
I think they are going to release the Switch Pro around March 2022, which means they'll probably announce it in January. That will give them a full year to ramp up production and phase out the old model.
This was my thought as well, the 1st party lineup this fall consists of WarioWare, 2D Metroid, Mario Party, Pokemon & Advance Wars. None of these titles seem like a good fit to show off upgraded hardware.
When the herd loses its way, the shepard must kill the bull that leads them astray.