1. USA is no longer sponsoring groundbreaking research 2. USA had already begun outsourcing research to companies that are not grounded in long term employment of researchers.
This is mostly about the new human-rated lander, which is an engineering problem. Notably, the US never had a reasonably safe spaceship, although Dragon may yet prove good. Both Apollos and Space Shuttles, developed under NASA, were pretty dangerous to their crews.
You’re absolutely right. Astronauts sign a last will and testament before every flight. We think it’s routine because we’ve nailed down orbital science but in reality, we lack the quality assurance that space flight demands. It’s one thing to send up robots and satellites, it’s another to send up humans. The ISS is crawling with bacteria. We lack the physical protection for long space travel for a mars mission much less visiting anything past the Kuiper belt.
I do think there are some novel challenges left for the Artemis project however that do require a lot of research and development before they are put before the boring engineering happens.
I think the real issue is that it's just still very, very hard. Margins are extremely thin. Airliners are extremely safe despite existing in a realm that's inherently dangerous because they spend margin on safety. You could make an airliner that's way lighter than what's currently flying if you didn't care about making it robust against, say, hitting a weather balloon. But the ability is there to protect against adverse events like that.
Spacecraft have almost no margin. The distance between normal operation and having a bad day is really small because getting people into orbit at all is still just about at the limits of available technology.