It's really hard to charge money, especially against a truckload of both free AND paid tools which do the job.
They decided to NOT charge money on the number of projects or the number of runners. They've made a product with no incentive whatsoever to pay for it.
We could say it's great, we get get another free tool! but how are they going to make this work on the long term?
They have no business model and the investor funds will eventually run out at some point. Then, we'll be left with another free open source abandoned projects, just like jenkins?
Their business model is the enterprise edition which comes with better support and newer "enterprisey" features first. It seems to be doing really well given their comments here. Gitlab.com is a loss leader to get their potential users excited about gitlab so they convince the potential buyers to pay for it.
Perhaps I'm in the minority but I have actually setup my home system to use SSO (backed via LDAP).
It annoys me no end that all these services seem to think that charging to maintain my userbase is a way to get me to think they care.
What it means is it invariably the SSO support is barely tested and poorly documented. For a number of products, I've tried out the "enterprise" version and realised that their features (e.g. SSO, audit, etc.) are just not useful.
Largely because there are not enough people looking at the thing or attempting to use it.
You seem to be focusing only on their public instance gitlab.com which is comparable to github.com. They essentially have the same model as GitHub(free for the community, payed for enterprise/companies). From where I am standing they seem to be giving GitHub some healthy competition in both areas.
GitLab offers unlimited private projects, and unlimited runners for CI right now.