Most of the reason given on this Loopscale hack could be considered a genuine course, though they are still criminals on whatever reasons, but i don't think hackers could hack this huge amount for fun. Hacking is a criminal activity and can't be for fun because it could land them in jail if they are. caught.
We have the right to pursue multiple conspiracy theories in this case.
1. Hackers only wanted to prove their capabilities by finding and exploiting a vulnerability in Loopscale protocol. Afterward, returning the misappropriated funds was done for self-preservation.
2. Handling the misappropriated funds from DeFi users is not easy at all. Hackers would face the risk of being tracked down and identified. Returning the funds to receive a smaller reward/bounty is a safer action.
3. Loopscale might just be staging a play to make its mark in the crypto market.
Ultimately, whatever the reason, DeFi users will suffer financial losses, lost opportunities, and wasted time. They should look for safer DeFi platforms to avoid such troubles and worries.