I'd expect a large part of it, like many companies, goes on staffing. Gitlab have 1300+ staff spread out all over the world, with all the various legal requirements for hiring and paying in so many countries.
Don't know if they still do, but they used to have fully public prometheus dashboards for their infra (no login required) and I expect many people would be surprised how lean the hosting environment was.
Obviously there is a raft of internal private infra not publically shown in dashboards.
With k6s and dynamic hosting I expect they understand minimising their Azure and Google cloud costs
Having their handbooks, code repos etc published and out in the open for public viewing they were a useful source for 'oh that's how they build it' automate it, template it as a reference for ideas and learning