Combined with very few restrictions on who could start a school and where. This has turned out to be a combination leading to consolidation of non-public schools into a few, huge conglomerates turning out a nice profit for their owners. How they make this profit? Make sure to establish schools in areas where students have good home conditions and need less extra support, also it's a good idea to have some higher requirements for starting like part of the classes in English. This means the students in need of extra help/worse home conditions stay in the public system, which will thus have higher costs per student (but our voucher system means that private schools must be paid as much per student as the public ones).
So even right-wing politicians think we need to change central aspects of this system, to prevent this kind of "skimming the cream". It is certainly no panacea
To my understanding (and I know almost nothing about it) there was a sex panic similar to the United States had a sex panic about pre-school baby sitting for toddlers and how the US version it was supposed to be due to a demon cult thing per this moral panic (pretty much disproved)
But somehow a similar but different thing happened in Sweden, I do not know the details, and the net response was school privatization?