Short answer: Because Libido and Sensitivity are both ridiculous trap stats in CoC whose only purpose is to make the game harder.
Long answer: As a game designer, variance is bad: you want to be able to plan an encounter as much as possible. If one player is going to go down in seven or eight successful enemy teases but another is going to get two-shotted by that same tease, which do you stat it assuming? Fengames are meant to be played with one hand, so they consistently assume that you should be able to beat the enemy even if you'll be two-shotted, and as a result the game is generally piss-easy. The one time CoC has a boss that's actually challenging, it's the Minotaur King, who for most builds is just outright fucking impossible to defeat because he's the only opponent whose design assumes you've maxed out your character and had the good sense not to crank up your minimum Lust and/or skyrocket your Libido.
Relegating Libido to a stat that only affects you out of combat, and excising Sensitivity entirely, eases the burden on encounter design tremendously and allows TiTS to have opponents and bosses that are somewhat more challenging than CoC's, if not enormously so.
Of course, the logical endpoint of this design methodology is to go statless, something I have endorsed for future projects but at this point would be difficult to retroactively implement for TiTS and to not much gain. As long as it's reasonably straightforward to max out your stats, there's no real problem since you can assume most players will have their build-important stats maxed at all times.