I took some time to check through Alexa Tomas' latest triple x ~Little Miss Fit
where half the clips are designated xxx and happy to see on average they are of longer duration.
If Totem are paying a higher rate per xxx clip
then it follows that cards devoted to all xxx clips would be unsustainable at current prices.
I agree with
@jefe2643 &
@KatzPaw.
..users would be more inclined to dedicate time to watch a few long scenes rather then A few shorter scenes, give more time to set the mood
imho there is nothing more distracting than a model interupting her good edging to orgasm ~ by some prescribed need from the studio for her to vary poses all the time in a clip, or to have her 'rising to a climax' session cut short to suit other clips.