If Phabricator was this, there would be no reason for paying customers to ever choose it over GitHub, because paying customers generally do not care if a solution is open source or not.
But the bigger impact of this change was not a product impact at all: it was that interacting with paying customers is something I generally enjoy and feel good about, and interacting with open source users is something I generally hated and felt miserable about.
For whatever reason, Phabricator attracted a large number of users who wanted to argue with me about every technical decision, insist that whatever feature they wanted should be the highest upstream priority, suggest I should pay them for their "valuable suggestions" because they are an important CEO, take offense when I asked them to please please please read the documentation and provide reproduction instructions, bump every open task asking for status updates, etc. This stuff had a huge net cost to the project and only got worse over time as the project grew.
Writing off open source installs allowed me to stop dealing with all of this.