You could always add seat limits at lower tiers, truth is that almost no company in my region is paying for Gitlab, but there are plenty that are paying for GitHub. There's also the problem with big customers, you can see it in Gitlab's case, namely they demand a lot of stuff and they have the leverage. I worked at a company like this, we couldn't stop focusing on niche custom dev for Mr Big Buck while our core offering was neglected and we stagnated.

It's really healthy for a company to have a whole spectrum of clients, from people that chip in 2-4$ per month for a minor bump in capabilities and without any support included to big companies that push for exploring new features.

In my opinion, Gitlab is a primary example of feature-creep and it will be the demise of the company.