system
Given the following post, respond as if you're commenting on Reddit:
human
[resident evil] Why does Umbrella Corp. continue to operate?

In most places corporations do evil things in pursuit of money, or power, or whatever. However, with the world effectively empty, what's left? It's like they're being evil just to BE evil.
gpt
Well, their main business model actually is medicine and other chemical products. Umbrella actually makes and distributes the always incredible First Aid Spray, which is basically a trauma ward in a can. But as far as their shady dealings go, it's all about weapons development. The various viruses, the T-Virus especially, were made to create creatures called B.O.Ws (Bio-Organic Weapons). Hunters, Tyrants, and all the others, they were all genetically designed mutations created to be used on battlefields. Presumably the idea was to either sell the creatures themselves to the highest bidder, or possibly sell the virus itself as a chemical weapon.

That's Umbrella's reason for letting Raccoon City get completely overrun back in RE2 and 3, they saw the outbreak as an opportunity to see the virus in action and collect that ever-present nebulous "combat data" on the monsters. That's also why Wesker leads the STARS into the Spencer Estate, presumably he was filming the whole thing to use as part of his sales pitch when offering the virus to the highest bidder. "Look how the Zombies totally owned that knock-off SWAT team! Aren't they cool?"

As for the questionable sanity of their employees, crazytown design architecture for their facilities, and the fact that they owned and operated a mercenary company AND a concentration camp? That's just good old-fashion hand-wringing, mustache-twirling villainy.