I doubt they'd just get rid of the old molds, and I doubt maintenance is an issue
Moulds are
extremely expensive to create and maintain and have to be chucked at the first signs of defect (LEGO Bricks are precise to 10μm, and any defect can ruin that and render a brick incompatible).
LEGO will usually archive at least one mould when a brick is no longer in active rotation, but not with the intent to use those moulds again, simply for legacy preservation. Benny's Spaceship is a good example of where a NUMBER of new moulds had to be built so they could redevelop parts from the Space theme that hadn't been used since the 80s.
and from what I remember most, if not all, of the lego brick creation is automated and actually pretty small scale for what it's producing
No, LEGO has 4 manufacturing plants and 4 packaging plants dedicated to operations (it should be noted that some of these are for specific types of orders; for example, the Czech one is for Pick-and-Mix orders IIRC), and these are loving massive factories. The actual process of refining the plastic pellets, moulding and sealing them, applying prints, cataloguing them, eventually picking them out for packaging and shipping is a MASSIVE undertaking.
Fun fact, I'm in the LEGO Worlds Special Thanks section. See if you can guess who.
