You actually touch on a good point: because educational success of a country is measured in the number of university* graduates, governments incentivize universities to, well, produce more graduates, which they do both by lowering standards for existing fields of study and by creating new fields that attract a lot of students but which don't really teach anything worthwhile.

The result is graduates are far, far less well educated than their predecessors but on paper (including, I would presume, PISA) a much larger proportion of the population is "highly educated", making the government look good.

To give an example of lowered standards everyone here can probably relate to: up until about five years ago, students at the school for applied information science where I work were required to learn (a bit of) assembly so they understood how computers work at the CPU level. This requirement has now been scrapped, resulting in applied information science graduates who don't know the first thing about how computers actually work. On paper, however, our school looks very good, because, after all, it is producing a larger number of "knowledge workers" than before.

* this goes for schools for higher vocational training as well