Devil's advocate checking in. By following your logic, it is utterly useless to know as much about the moon as we do unless we are planning to go back there. And there are very, very good reasons to go back to the moon first.

It is a whole lot closer, therefore easier to access and easier to build upon.

It has raw materials that could be extremely useful in building ships, and also in building the factories to make those ships. Even probably water, and if so there's rocket fuel to be had.

It has a far lower gravity, which makes getting anything you build on the moon a lot easier to get off the moon, especially as compared with trying to do the same from Earth. Even if we were to assemble a ship for Mars in Earth orbit, we have to get it out of Earth orbit, which means a higher escape velocity which in turn means more fuel and bigger engines to push that large, heavy ship around. If a similar-sized ship was built on the moon, or in lunar orbit, it would not only need a smaller push but could use a neighboring gravity sink (Earth) to pull it in, build velocity, and slingshot it back out.

NASA and others keep talking about getting into the asteroid lariating business, especially with an eye to anything that contains water. It is immensely inefficient to lift water from the Earth into space, but at present it is an absolute must as nothing else can happen without water being available. A lot of these plans for lariating asteroids tend to involve parking them around the moon. It is a good stable orbit, it is not too far out, there is a nice safety feature in having them parked by something powerful enough to reign them in rather than have them fall on Earth, etc. So, if you do have extractable water in Lunar orbit, why wouldn't you build there?

TL;DR version: Columbus didn't build his ships in Madrid and drag them overland to the coast before sailing for the Indies. Going to Mars and building ships around Earth is like building them in Madrid. Build your ships where the tides can help you on your journey.