> There might be a "value" in it but why shouldn't they pay for it?
It is called an investment. Society invests in an individual education because in the long run that individual is going to be able to contribute more positively to society, returning a greater value than the initial investment. A better educated society takes better decisions, is more creative, adapts faster to change... Why shouldn't countries invest in its own future?
If citizens have to pay for that education maybe they are not going to be able to afford it, or just are not going to do that investment because they lack the education to understand the benefits. The situation becomes a loss for the individuals, but also for the country.
To treat education as an expense is a mistake. That same happens with, for example, infrastructure. If you treat it just as an expense, why do the government build roads? The reality is that a country without infrastructure is as badly prepared as one without educated citizens.