In order to understand any reasonable sized piece of software, you need more than just the code.
You need the known bugs - verified and reported with all that entails.
You need the architectural vision and how that is expected to be changed over the short and long term. You need to understand the complexities of the architecture you have versus what the vision was and is supposed to be later on. There’s never an exact alignment from what was planned and what was built.
You need people who do know the guts of the thing to manage commits and review. That’s a HUGE effort. I’ve seen comments from quite a few people in these roles on other larger open-source projects and it takes a LOT of their time. And they can get burnt out which is awful when you then lose a key player.
Open source projects are no better at finding serious security bugs (in 90%+ of the open source projects, there isn’t enough security expertise) than other models of development. There is more disclosure, but that only happens after you identify and that still takes expertise that most projects don’t have.
Opening up a small project with a few key developers leads to more time spent fighting religious wars about how things should be done. The larger the team, the more fights and wasted time. And in open source, if someone has the hammer and calls the ball… it can lead to a lot of disgruntlement from devs who are trying to help but who have gotten their head down in the weeds and that just are so certain of some design aspect that they just can’t let it go.
Silver and other key players have done as much as they have done and they have done it well. There’s no clear benefit to the product to open source and even little or no benefit to the customer base. Some folks would like X, Y or Z, but that’s a very individual want in most cases.
I would not want them to go open-source unless the business was ending and they were going to put the existing code and knowledge into a perpetual open-source repository that someone might want to take on.
Some of the best software I’ve ever used was written by 2-10 people.