Developers are businesses and the economics need to work. For that, safety and security is much more important than openness.
Meanwhile, you're not looking at those who left, or those who decided to never enter a broken market dominated by players convicted of monopolistic practices.
This seems much more intuitive than a hypothesis where somehow people would prefer to enter a closed market over a fair and open market with no barriers to entry.
Remember, monopolists succeed because they are distorting the market, not because they are in fact the most efficient competitor.