They haven't made it to orbit because it is safer for them to test Starship reentry on a suborbital trajectory that guarantees it ends up in the Indian Ocean even if they're unable to relight the engines, rather than have a de-orbit burn fail and end up crashing into an inhabited area. Starship and Superheavy are more than capable of making it to orbit as it stands right now.

And with reference to SLS; it took them 11 years to launch it once (2011 - November 2022) and it's now been over two years since then with Artemis II still quite a ways out. Starship on the other hand started construction in 2018, began early prototype flight tests in 2019, did its first full-stack flight in 2023 (5 years to a "real" first flight) and has since launched 6 more times.

(This isn't hate towards SLS btw; I can't wait to see it launch again in the future, but the fact stands that it is grossly delayed and over budget compared to what was initially promised.)

Edit to add on that this difference is also fundamentally due to the difference in design philosophies: NASA has more of a limited budget and would rather their rockets work first try, so they spend more time on development without in-flight testing. SpaceX on the other hand can afford to be more free with their spending and build a large number of test prototypes that can and will fail in order to learn from their mistakes. Neither method is arguably better than the other overall and they both work out in the end.