Computers are not the problem here. Orbital mechanics are same as they were in 60s and 70s. You just need basic math to calculate how to get to the moon.

Costs are the real blocker. Back then costs did not matter. Moon race Was another level of cold war. Right now everything is way more expensive and NASA fight battles each year to get budget from the US which they rather want to spend on space exploration which can be done unmanned and can lead into new findings and push science forward.

There is nothing interesting left to be found on the moon so it's not a priority.

Space probe is pennies in comparison to send people anywhere outside of atmosphere.

Simple as that.

Artemis mission is more about learning how to live outside of Earth and establish another space station on higher orbit than just visit the moon once more.