Distaste with the effects of emphasizing competition while at the same time awarding rank and teaching positions based on competitive results.... honne and tatemae maybe?
I think more of a growing understanding that the emphasis on competition was getting out of control and twisting the entirety of Judo into something he did not want. Unintended consequences I suspect. The Kodokan made it's name in inter ryuha matches and so placed great emphasis on demonstrating that your technique worked under those conditions. Over time any other reasons Kano may have originally put forth for competition were forgotten in the dash for competitive glory and rank earned in competition. Since Kano set up the Kodokan as a modern organization run by a board of directors that he didn't choose, it soon was out of his hands. I think the fact that he never supported making Judo an Olympic sport is relevant.
Unfortunately, I have neither the money to buy, nor the time to read, the 14 volume complete collection of Kano's writings. It would be interesting to see if his changes in opinion could be traced through time.