Why can slavery even exist in 2021?
Depends what you call slavery.
Today I personally would call slavery any low-paid labor that nobody wants to do.
On the other hand it's labor you do at minimum not by your own will (you can agree to work cheap if there are no other options).
In any case such labor still exists, even in the most European Europes.
If I were a slave owner, which of my tasks would I delegate to slaves today?
Only those where the quality of the result is completely unimportant to me, the fact of performing at least some part of this task is important, because for obvious reasons a conditional slave won't do the job well and efficiently.
It turned out that personally I don't really have such tasks - everything I do in my life requires a quality approach. Why then does slave labor still exist?
Let's take an obvious example, the sex industry. Why does slave labor still exist in it?
Because today consumers have an unsatisfied need - a need for at least some sex. Not quality, but at least some.
Surely a man who already has at least some sex or money won't use the cheapest prostitute - he'll go specifically for quality, specifically to that prostitute who's motivated to perform the service with quality.
Such a one will most likely be working at such work by their own will, i.e. we won't consider such labor slavery anymore.
So we're the government. How to solve the problem that slave labor in the sex industry even exists? Make it so the potential consumer starts being interested exclusively in quality.
This can only be done by starting with culture. If you explain to the consumer that it's fashionable not to have lots of sex but to have at least one but quality one, then he won't go to the cheapest prostitute.
But how to explain to today's consumer of cheap sex that quantity doesn't matter when the idea of quantity pours on him from every corner?
Need to give less airtime to those who promote the idea of quantity and more to those who promote the idea of quality.
How to do this?
Given we live in the age of new media, content is delivered and distributed by algorithms.
That's how from the question of slavery we again come to YouTube and Facebook being bad.
What to do in a case when conditionally an American company delivers content that sex is great, cool and awesome to a fourteen-year-old Filipino?
No way to do anything, who even needs him.
Conclusion, strangely enough:
modern problems require non-standard modern solutions.
Often any problem, whether warming or slave labor, can only be solved by a culture shift. And how to shift culture in a given year (in the 60s you had to sing songs, today - outsmart algorithms), that's the big question for a smart person of their time.