Maybe somebody has asked this question - if so, I missed it - but what do you mean by "officially?" Do we have an actual statement from Canon? Do we have actual sellers reporting that Canon has told them these lenses are being discontinued? Or are you just speculating that "Sold out" or "Unavailable" means discontinued? That seems to be the most important question that should be answered.
If these lenses are being discontinued, it seems obvious that the reason is that sales numbers are way down or non-existent, regardless of how popular the lens might have been at one time. My guess is that those buying the latest DSLR's (The 1DX III and the 5D IV) are users that were already in the FF system and not buying new EF lenses in any substantial number. Canon would have that info, and clearly they will use the time and facilities they have to produce what is in demand now - and that is RF lenses. Would you schedule manufacturing time making EF lenses when your R5 and R6 Cameras are selling beyond expectations and lenses are on backorder everywhere?