I get what you're saying about worse conditions existing in the world. I see them most days when I travel about my current workplace.
So how much of the 3I is a dystopian future, and not a bright and shining city in the sky?
There may be tens of trillions of people living in TLC+ systems for whom this is not an issue, but has anyone crunched the numbers on how many worlds in, say, the Spinward Marches could be like this?
The really shitty conditions are probably *relatively* few and far between - as are the shining cities on a hill, in all likelihood.
I´d wager that, the further you are from the centers of power, and thus from the center of attention of those holding the power, the more feasible debt slavery becomes as a business model. New colonies located in the butt-end of nowhere, small-ish scale mining operations in otherwise uninhabited or low-pop backwater systems, that sort of places - anywhere they can keep these things under the radar. Even if they aren´t illegal, they´re bad publicity, and at the very least, publicity scares away the suckers who would fall for that sort of contract.
Besides, those debt slaves are still Imperial citizens, and the Emperor and his vassals have some sort of obligation to look out for their welfare to some degree. The Third Imperium and its nobles and government aren´t angels, but they are pragmatic (allowing this shit is just bad for society, overall) and have a certain basic sense of decency and honor. Sure, that thing is legal, but there are things feudal overlords (who also wield a lot of economic in addition to political power) can do to the perpetrator of sleazy-but-technically-legal schemes that persuade them to change their mode of operation while still falling short of clapping the malcontent in irons and leaving them to rot in the dungeon. Barring all companies involved from receiving government contracts, for example.
The Third Imperium has 11,000 worlds; if their populations were all randomly determined, that works out to roughly 3,000 low-pop worlds, 1,000 high-pop worlds and 7,000 worlds in between.
The high-pop worlds are too much in the limelight and too integrated into the Imperium-wide exchange of information to be good places for business practices that, while not illegal, will ruin the reputation of your company if it is even remotely involved in this - I cannot imagine that the press in the Third Imperium is any less inclined to publicize scandals than ours today is.
I´d say that the great majority of the mid-pop worlds and at least part of the low-pop worlds are out for the same reason, other than very limited local operations in remote regions of the mainworld, in asteroid belts or on planets far away from the mainworld - essentially places that can avoid the public eye, no passing traffic, as little outside contact as possible.
So, I can´t see a very large number of systems where some sort of debt-slavery is happening more or less system-wide. A couple dozen Imperium-wide, maybe? Add scattered little local operations here and there, such as the one described in "Expedition to Zhodane".
The total population of the Imperium should work out to something like 22 trillion. I´d estimate the total number of people who are victims of debt slavery somewhere either in the millions or low tens of millions. A relatively remote region such as the Spinward Marches probably has a somewhat disproportionately large chunk of these. So... I dunno... a couple dozen operations, total number of victims in the low millions?