Probably because it was one of the tests they removed a while ago (they removed maybe 90% of the tests). They did say at the time that SEO Skill Assessment was one of the ones that would stay but it seems like they’ve removed it since then.
Do you have an idea why Fiverr removed this test?
It’s probably a similar thing to what they said in this link:
We regularly evaluate our products and features to ensure we have the best buying and selling experience and will continue to update you as we make changes…
It might also be due to the cost of the tests, since it costs Fiverr every time someone does a test (since it’s a 3rd party that does the tests even though there’s probably some API or something that allows Fiverr to run them on the site) so maybe they want to reduce the amount of them to just the ones they think are most needed to save money.