The interesting part to me here is that all the non-open source tools are very big, successful companies
It's quickly becoming clear (GitLab/Mattermost/Sentry) that there are some great ways to build enormous companies like this though. And, that's of course assuming you want to build a huge company :)
At a personal level, we found that this kind of business is just more fun to build... making cool stuff in the open and if we do a good job, getting inbound interest from bigger companies that have developers who need to use our tech at scale.
I don't think it'd work for everything - if you are a tool that developers don't interact with much, then I'd imagine it's tougher to build a real community.
on the other hand, SaaS products are optimized to sell to business groups who want the hard parts taken care of for them and they perceive value in saving time/money thanks to the SaaS product. I've seen both situations (monetizing open source versus monetizing a SaaS product) first hand, and it's clear that open source companies can be at a bit of a disadvantage. If they DO monetize their users, it's usually via their own SaaS offering to augment the open source tool.