The Master Chief wears so much armour he could surely barely move, which serves also to highlight the contrast with Cortana's choice of clothing.
Or lack of, as she doesn't wear any. 343's Halo franchise director Frank O'Connor has in an interview with GamesRadar tried to explain the disparity.
"She's not really nude … but that's what it makes you think of," he said. "So one of the reasons she [chooses to appear without clothes] is to attract and demand attention. And she does it to put people off so that they're on their guard when talking to her and she has the upper hand in those conversations.
"It's kind of almost like the opposite of that nightmare you have where you go to school in the nude. You're terrified and embarrassed and she's kind of projecting that back out to her audience and winning intellectual points as a result."
Which makes you wonder why the Chief doesn't employ this tactic too, if indeed it is so formidable?
What seems more likely is that Cortana is nude because she's female. And if you're female in a video game that seems to be how you're often depicted.
To refresh your memory, here's Cortana:
Here's another physical female AI embodiment – EDI from Mass Effect:
How developers choose to depict their female characters is a hot topic because the industry is at long last waking up to its inherent problems with gender inequality both within its offices and within the worlds it creates.
Only recently Hideo Kojima kicked up an almighty fuss over his treatment of The Phantom Pain character Quiet. Here she is:
When people started asking questions about why Quiet wears almost nothing while buddies Snake and Ocelot cover their privates, Kojima made out like the sceptics were fools.
I know there's people concerning about Quiet but don't worry,” he explained at the time. I created her character as an antithesis to the women characters appeared in the past fighting game who are excessively exposed. But once you recognize the secret reason for her exposure, you will feel ashamed of your words and deeds.”
The explanation? Quiet breathes through her skin, therefore requiring her to expose as much of it as possible.
Were Quiet an actual human who actually breathed through her skin then no-one would begrudge her trotting about in the nud. She's not, though. She's a fictional character with fictional 3D modelled baps with a backstory written by a man specifically to justify said tit and arse exposure. In the same way that Cortana, and any conjured backstory, is designed and modelled by men for men.
Incidentally, it's not clear if Quiet's skin-breathing is also the cause of her in-game helicopter frolics:
Or her rain dancing:
Or the hidden shower scene. Yes, there's a hidden shower scene:
But the men surely behave the same way, right? Because there's no way Kojima has Quiet behave like this due to her gender, right? Wrong, although modders have stepped up to highlight exactly how it would look if they did.
Here's Ocelot frolicking in the rain:
And freshening up: