IMO, the situation with Canon and 4k video is the same as Canon and DR. They dragged their feet with on-chip ADC just like they have with 4k video. When they could no longer keep using poor DR sensors they ponied up and made the improvement. The same situation is here for 4k. They have ignored it for as long as possible and now feel they have to give this ability so as not to take a serious hit in market share. The same goes for AF ability in their MILC cameras. We had the M, then the M2 and the M3 before they got serious and gave us decent AF. The roll out of the M50 is Canon finally capitulating to the consumer demand for 4k and the desire to keep, or increase, their market share.
I think most of Canon's late response can be traced back to their delayed response to mirrorless as a whole. Sony, Fuji, Panasonic and Olympus put all their efforts in mirrorless because they didn't have a choice. Canon on the other hand wanted to see if the whole mirrorless thing was just a passing fad or something more serious. When Canon finally jumped into mirrorless they only had Powersot technology to start with.
On the other hand they knew someday 4K (or 6K, 8K) will become a common feature in consumer grade cameras. It is difficult to know why Canon dragged their feet this long. I think it's probably because of a combination of not having the technology to put 4K in a small body with good heat management and treating 4K as high end feature even when it was clearly not.
DR probably is the most debated issue in internet forums. Even to this day most don't care about it, don't use it or don't know how to use it properly. But it became an image issue (to some extent 4K is similar) for Canon. But it is difficult to say if DR was the only reason Canon moved to on chip ADC.