Finnish students get allowance from the government for the duration of their studies (max ~60 months) and get government backed cheap loans which they start paying back after their studies.
My own experience is that there are people from very varying backgrounds in the Finnish universities.
Thought experiment: American students also get government backed cheap loans. Further, since these government-backed cheap loans are often used to cover cost of living as well as tuition, they are a de-facto allowance from the government (albeit one you need to pay back after you are graduated). And yet the american education system seems to have a bunch of dysfunctions that the Finnish one does not.
There has to be other differences that cause this, it can't be the presence of cheap loans. The conventional wisdom in America is that cheap loans incentivize universities to raise tuition, because they know the money is still coming in. Why does this effect not take place in Finland?
When the government is directly covering the cost of education, they are the ones bargaining with educational institutions. If the institution tries to bump prices, the government can pull funding for that institution and basically eliminate their revenue. As such, the institutions and government are required to negotiate much more rationally.
The question should not be "what is different between the systems?" but "what, if anything, is similar?".
If the university finances are decoupled from student ability to pay, then loan availability doesn't distort the education institutions, but instead mainly affects the lifestyle of students and their families.