Some of it could boil down to efficiency/planning. It could take me years to code a game engine, but if I write it correctly, I should be able to go in and update parts of it without having to do a total rewrite. If they have an established library of simple objects (code) they could theoretically plug in bits of code and only work on things that need to be updated. Most game inventory systems can be pretty simple. You could almost use the same inventory system for every game ever made actually. If you constantly re-code this specific for one game, you might save yourself some time upfront, but you'll pay in having to re-code it for the next game. The same applies for many aspects from weapons to characters to AI.
It seems the mods need help with this forum. I have zero tolerance for trolling, platform criticism (Rule 4), and poster bad-mouthing (Rule 3.4) and you will be reported.
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