I am torn between admiration for Canon making the TS-E 50mm lens (and a 2.8 and Macro at that) and bewilderment that that has been given a high priority than a modern 50/1.4. That TS lens will have been very involved to design and build, inevitably will not sell that many units but speaks to canon's determination to maintain an ecosystem that nobody else can match with the highest quality glass. All great. But still, yes, the OP makes a fair and funny point - a modern 50mm 1.4 , L or non-L would seem a no brainer.
I suspect some of this is because of Sigma's success in that focal length perhaps having now saturated the market for those wanting a fast sharp modern 50 - if Canon is doing serious market research I think they might find that there just isn't a huge demand. Those who really want a 50mm L lens in many cases already have the 1.2. Those who just want a simple 1.4 can buy the lens sold today which is good if not great. Those obsessed with sharpness can buy the Sigma 50 Art. So while many here - myself included - love the idea of an updated 50/1.4 with L build quality and maybe IS, how many of us would actually be willing to pay the high price Canon would likely charge to recover the development costs?
If the number who really would buy it is low then Canon simply will not be pushing resources that way. I am sure it will come eventually, Canon clearly is determined to maintain a high quality range of glass, but I sort of understand why it would be a lower priority.
For me the strangest thing really though is why they don't make the 50mm 1.0 again. The old lens, impossible to service, soft at wide apertures, terrible bokeh, clumsy auto-focus sells for thousands second hand. If people could buy a brand new one from Canon, hopefully improved especially with modern coatings, and full warranty and ability to service it, I am sure these days there would be more demand than before. I think more and more people today are willing to pay thousands to buy what they consider to be "the best" - see how Zeiss has made a success of the Otus line. If Canon wished to avoid development costs they could simply restart production of the flawed original I think they would still sell plenty - they could price them at $3000 and undercut the second hand price which is rather strange!