See this is my take on it. With Caroline and the MC, yes they do want it BUT Caroline isn't looking just for sex. She want's a legit relationship between her and the MC. Up until now their relationship was governed primarily by the deal and was mostly physical. Now shes accepted her feelings for the MC, she wants to make a legit go of things hence the date. At the same time though shes aware they already done more than most "couples" have by that point in their relationship hence the blowjob.
With Linda and the MC, their relationship is one primarily ruled by lust/physical desire. Linda has lusted for him from day 1 of the game, he's the one whose feelings needed to adapt to that. Now they have, they've both admitted their feelings to each other, they've done the foreplay, now they gotta do the deed.