that's why

Earlier I saw one of those side-by-side comparison 'what-is-wrong-with-this-picture' photo sets comparing a brothel to a prison somewhere in Germany. The prison was modern, new, clean, well-built, well-equipped, and all-around a more accommodating place to spend your days than the cramped, dirty, dilapidated brothel. Obviously it was meant to show how much better prisoners were treated over sex workers in a 'why-is-this-okay' sort of way, but I didn't even have to go past the title to come up with a reason this is an unfair comparison.

First of all, old buildings semi-remodelled for another purpose are the norm in most of Europe, which is smaller and much more crowded than the Americas and has been built on continuously for thousands of years. Easier and cheaper to fix up something that's already there than it is to rip it down or find somewhere to put a new one.

Though hardly an unreliable indicator, the condition of a building is in no way automatically indicative of the treatment of the people who live/work there.

Budget--it said nothing about this, but odds are a prison has a much bigger budget in both construction and maintenance than would a brothel.

...and the brothel isn't built for the use of quite so many people.

A prison is a public institution. A brothel is not.

The biggest reason the comparison is misleading and unfair is this: with few exceptions, a brothel is unregulated and a prison is regulated. There are authorities, codes, and standards that by law have to be met and consistently upheld in order for a place like a prison to be approved for its intended use. It has to be safe, adequately heated, and reliably plumbed or the government will (at least in theory) shut it down and pronounce it unfit for use. This is the story for all buildings of every kind intended for human use and/or habitation, but especially true for taxpayer-funded institutions like prisons because, with everyone helping finance them, the standards are placed much higher. In most countries, there aren't any such rules for brothels or other back-alley operations--no government authority making sure they are safe or reliably maintained or free of asbestos. Without laws governing them, they're free to keep their inmates/workers in whatever conditions they feel like without legal consequences. This is why you see the government declaring buildings unfit for human habitation and condemning them, only to have them snatched up for use as brothels, drug labs, drug dens, chop shops, salerooms for stolen goods, and other illegal operations: there's nobody stopping people from using unsafe or dilapidated buildings or keep a consistent standard for their workplace and/or employees when the operation itself is illegal to begin with. And hey, a condemned building comes with certain clear advantages, like not costing anything to rent and being, at least on paper, empty.