system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU]When up against Thanos et al, why don't the sorcerers of Earth use portals as weapons?

For instance, we saw how Cull Obsidian could neatly have his hand chopped off by one, and Thanos was obviously too physically strong for any of the Earth-based superheroes to beat in a fist-fight, so why didn't Strange and his pals just open up a portal around his waist and then just close it off?

I appreciate that not wanting to kill is normally a factor that would be part of why portals wouldn't be used in this manner, but with Thanos and his minions/army, surely the gloves were off and anything goes?

Is there any actual reason why this can't be done?
gpt
The directors have said that Thanos's skin is too tough for his arm to be chopped off by a portal. Of course the more logical answer would be that Thanos has the Space and Reality Stones every time he fights Strange, so he could have used either of those to avoid the portals cutting his arm off, but the directors decided to say that Thanos could just withstand the force of space collapsing down on his arm.