It's not like every problem in space is running out of oxygen in 90 minutes. I can imagine plenty of scenarios where having additional resources in the matter of days vs months would make the difference in a life or death scenario. Especially if we were able to establish a decent support network on the ISS or other space stations.

Not to mention you would be able to realistically cycle out astronauts on a moon base, whereas being assigned to a mars base would be a one way trip for many.

We don’t even know whether people can maintain health in microgravity making enough to get to Mars. We don’t know if they’ll be functional when they get there. We don’t know what level of gravity is needed to maintain health. We don’t know odd people could survive the radiation for a trip to Mars.

Let’s figure some of these out in a shorter trip

Hmm, I think a huge thing you've overlooked is using the moon as a staging area like maximum Derek said above. We stockpile fuel, food, etc. And maybe even begin to manufacture vessels there to save from using a vessel stressed from an earthly launch. Would make Mars trips easier, asteroid missions, the like

Edit to add: I wouldn't be surprised if there's still some forms of metallurgy or other processes that can be discovered with a continuous scientific base on the moon, that they couldn't attempt on the ISS or replicate here in vacuum

The Moon is great because of close proximity to Earth (communication, and logistics), and because of low gravity.

Space launches are expensive because of gravity. Mars is similar to Earth in that regard. To launch from Moon, we can use electromagnetic launchers installed on the surface, powered by solar panels or nuclear reactors. To launch from Mars, we need chemical rockets which are mostly fuel, like on Earth.

If we ever want to do space exploration or even space industry on scale, we need to get away from chemical rockets. We either need to make something like a space elevator / hook / sling / whatever, or locate the assembling industry and launch facilities outside of the massive gravity wells of planets. It's hard to imagine humans launching more than a few probing missions to Mars or asteroids, without simultaneously developing a Moon base which can support more than that.

The Moon is a place close to home where we can mine certain materials, assemble our spaceships, and launch missions to everything else in our solar system. A bit like an airport outside of a big city. No one goes there because it in itself is so interesting, but because it makes it easy to get to other interesting places.

The Moon still has properties on top which make it interesting, like doing radio astronomy from the other side, which is shielded from terrestrial radiation.