I think Harris clearly laid down a marker not only for Brown, but for the Process itself. Translation: it must finally bear real fruit or I'm going to consider a different direction. His previous moves to short cut the Process speak for themselves - firing Hinkie, hiring Jerry's son, taking over a year to hire a new GM after being forced to dump Jerry's son, hiring Brand who had zero experience, dumping Fultz, bringing in the expensive vets etc.
In Harris' mind, IMO, he has spent a lot of resources and time on this Process and it is due on delivering results. Firing Brown would, in that mindset, be the next logical step and open the door to a roster shakeup to demand accountability.
All the 76ers marketing for years has been of an "emerging power" and "great times are here again". If the team cannot win more than one series a year in the playoffs, that does not match up and the shine starts to wear off.
I could be wrong and hope I am, but I do not have any illusions about why Harris owns a basketball team, that he seems to be a meddling owner and that he is not patient enough, as he has shown before, to let the Process work out unless consistent progress is made.