Is there no reason to colonize the moon?

No, there is no reason.

It was suggested we might build a base there to send people off to Mars.

Alas. No one’s going to colonize either place. The moon is a vaccum and Mars is poisonous and dead.

Aside from Hollywood, there is no reason to colonize either place. We can and will send robots to do our work of exploration there. Human footprints there are useless except for photo ops.