Being an all-remote company allows team members to choose to live and work where they want. This benefit provides folks more choices when deciding where to live and work.
"No, this is Netherlands only since this is easier for GitLab Inc. to do. We have more team members in the Netherlands and we got accepted in the local European Blue card program years ago (after a business plan review by the government, it wasn't trivial at the time I remember)."
Normally a work visa requires a local "visa sponsor" or employer so Gitlab would only be able to offer relocation to countries where they have a fiscal presence.
CEO is Dutch and probably has a Dutch entity. Work related immigration is relatively easy for Netherlands, especially compared to USA. Recently the salary requirements have been lowered.