Because nobody ever got sucked into the sand without much explanation in any other movie? Lawrence of Arabia and Max Max Beyond Thunderdome spring to mind.
Pointing to other movies as an excuse (especially Thunderdome) doesn’t really cut it. And I love Mad Max.
I actually didn’t think much of it myself, and I didn’t even remember Rey’s line about quicksand. It’s just an example of lazy writing (“we need X to happen, so let’s introduce Y a bit earlier”), and the least egregious in TFA by far.
The Stormtrooper sword fight was just dumb. Finn swinging around a lightsaber against an experienced Force user was dumb. Darth Vader’s torched mask could’ve beaten Finn with less difficulty.
And now that we have inanimate objects serving as vessels for the Force, why not? Vader’s mask can go head to head with Luke’s severed hand in Ep. VIII. Yellow Yoda probably has that in a chest someplace, along with Luke’s X-Wing keys.