Actually prostitutes themselves clamor to make their business legal and by and far aren't the 'victims' the media tries to portray them as.
Here's the issue.
What does legalisation mean?
Short answer, legalisation doesn't mean legalising the act of being paid for sexual services, that's typically already legal by the point a country is considering legalisation and even when it's not legal is unenforcable. Neither does it mean legalizing loitering or public solicitation, which are the actual crimes people get arrested for. Those typically remain illegal because they're considered a public nuisance.
What legalization actually means is legalizing brothel ownership, escort services and things like advertising sexual services openly. In other words, what is being legalized is makjing money from prostitution by controlling a business that employs or takes money from sex workers.
And every time this happens, there are some consequences. Most notably, demand for sexual services rises enormously, but the supply of people (particularly women and trans people) willing to actually do the work generally does not. There are not a huge mass of people clamouring to work in brothels. Those who do end up working in brothels are typically either immigrants, who are brought in specifically to work in the sex industry, or people experiencing financial hardship who see it as a temporary solution. A few people who work in the sex industry end up liking it, I know quite a few people who did sex work or thought seriously about it and for most of them it was a pretty good and empowering decision at the time. But what most of them found rewarding was not only the financial reward, but the freedom. The more forms of rent you have to pay, and the more beholden you are to a business which expects financial return on your work because it has rent and salaries to pay, the less that freedom exists.
Now you might say, well that's fine, as long as the rules are enforced the market will just sort out the labour shortage. But what happens when demand rises but supply does not? If prices were to rise, then it would become unaffordable to many people, but those people still have demand, so where do they go? Who meets their demands?
Legal brothel ownership and organised crime are not entirely separate issues. If they were, it wouldn't be necessary to screen legal brothel owners for previous human trafficking convictions. The people who will inevitably end up running and profiting most from a legal sex industry are often the same people who were doing it before. Except, it becomes far, far more profitable because of demand, and far safer from legal scrutiny.
In short, the sex industry is capitalism. Capitalism is not a nice or benevolent system. It does not exist to protect the right of workers, nor does it inherently place any value on the rights or quality of life of workers. If you create a highly regulated legal industry, people will escape regulation by creating an illegal industry, just on a much larger scale than before.
There's this idea (and bear in mind a lot of discussion of the legal sex industry comes from PR) that legalizing prostitution will move people off the streets and into brothels where they will be safe and protected. That may occasionally happen to individuals, but the reality is that really vulnerable people will still end up on the streets (in greater numbers), because they can't afford to pay rent to work in a brothel, because they or the people controlling them can't afford or don't want the scrutiny that comes with regulation, and because ultimately the problems of prostitution are caused by demand. If you want cheap bodies, you can get them cheaper by abusing people.
Not to mention prositutes also service quite an amount of people that are handicapped or otherwise disabled. Denying them any kind of physical intimacy is also cruel.
I also can't help but feel that the idea that access to another person's body is some kind of right to which everyone (everyone male at least) is entitled and which it is unbearably cruel to deny them has a slight whiff of inceldom about it.
The fact that someone can choose to give sex or physical intimacy to someone who would otherwise struggle to find companionship is a pretty positive and neat thing, but what's positive about it is the choice, and the merit of making that choice. The supposed injury or harm of not having easy access to sexual partners does not justify any kind of insinuation that a person is owed sex, and that the provision of sex is some kind of duty which women as a class owe to the male population.
