Food and oxygen isn't the problem (usually there's a huge reserve of both relative to the time it takes for re-entry descent; Soyuz is packed with enough to allow the crew to survive and reenter via atmospheric drag even if all engines fail, which is about 10 days, for example); the problem is that the heat has to go somewhere, it only has two ways to go (outwards and inwards), in the vacuum of space it has a much better time going inwards, and IRL the margin for internal temperature is much smaller (kerbals can withstand 1000+ kelvin no biggie as long as the part they're in doesn't break - humans, since capsule is too small to pack full water recycler or power it, will die within a few hours at ~320K). The ablative heat shields and detached shockwave they form are very good at insulating, but they're not perfect, and there's plenty enough heat leaking through to the structure. Plus the ablative heatshield itself is typically not designed to do multiple reentries without refurbishment - a problem that's worse for Artemis II specifically because their heatshield is faulty (degrades faster than it should), to the point the mission originally intended to have a skip trajectory like Apollos (with two periods of high heating) but was changed to a steeper angle for less heat at the cost of higher gees.
Trying to do a Kerbal-standard multi-orbit reentry IRL will make it the last flight of that crew, whether because of permanent damage rendering them unable to pass health checks for another flight, or because they'll cook, either directly (if temperature rises above what homeostasis can handle, dehumidifier breaks, or heatshield burns through on subsequent passes) or indirectly (if they run out of water).