Flaking Pain On Metal Window Frame

I am renovating my basement and noticed the 2 window frames have a metal bottom frame that have metal flaking off. My idea to resolve the issue is to use a small hand sander to remove the flaking paint and simply use a paint brush to put a new layer of paint. I have a few questions:



1) Why would metal be used?

2) Why is it flaking? I don't notice any moisture nor do I see any damage to the sheet rock

3) Can basic interior paint be used (e.g. ceiling / flat paint)?

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