The work is difficult and the visible payoff low.
It's easier to play a video game and get a good feeling out of that than reading and trying to understand this:
1. Pleasure and distress, fear and courage, desire and aversion, where have these affections and experiences their seat?
Clearly, either in the Soul alone, or in the Soul as employing the body, or in some third entity deriving from both. And for this third entity, again, there are two possible modes: it might be either a blend or a distinct form due to the blending.
And what applies to the affections applies also to whatsoever acts, physical or mental, spring from them.
We have, therefore, to examine discursive-reason and the ordinary mental action upon objects of sense, and enquire whether these have the one seat with the affections and experiences, or perhaps sometimes the one seat, sometimes another.
And we must consider also our acts of Intellection, their mode and their seat.
And this very examining principle, which investigates and decides in these matters, must be brought to light.
Firstly, what is the seat of Sense-Perception? This is the obvious beginning since the affections and experiences either are sensations of some kind or at least never occur apart from sensation.
Especially because most people have no use for theoretical metaphysics in their life. Easier to let Aquinas do it, the Church to promulgate it, and follow the rules based on the conclusions.
On top of that, the average IQ is 100, and really that's not necessarily enough horsepower to get very far in this stuff without tons of extra work (which I am willing to do). For people with high IQs, it probably comes easier I would guess.
I think it comes down to cost-value. Most people won't get a value out of it that surpasses the cost.