Or he realized it was making him pander in a way that was unprofessional and wished to stop it.
Some of the greatest music compositions ever written (Bach's Mass in B Minor, and Bach's Chaconne) were not written for the approval of an echo chamber. They were written to satisfy his personal notions of beauty, and in the case of the Chaconne, to record his feelings about his life with his wife. In fact, incredibly, they were never performed while Bach was alive.
When Bach wrote for approval, for acknowledgement of form, you got things like the Brandenburg concertos. Fancy, showing off... Bach made sure that the listener would not have to work at all to see his adherence to form. They are lesser pieces of music because of this.
Mr. Podhoretz is not the J.S. Bach of the written word. But even so, what art he possesses necessarily suffers for being expressed in the panderdrome that is Twitter. Do it for long enough and it diminishes you.
TLDR: You should quit tweeting if, like him, you tweet 50+ times a day and you occasionally tweet obnoxious insults or bad jokes which get you ratioed.
Sounds more like he was forced off the platform.