Because it's a graduate tax rather than a debt, if you do well then you will pay more until you've hit a cap, if you don't make that much then you're not in debt.
Education in other EU countries is free because of some combination of greater selectivity (i.e. a significantly lower proportion of people go to university), or because it's lower quality, or because it's necessary to make up for the lower quality of high school education.
You could solve the fees issue in the UK by reducing the number of places for domestic students, however this could go quite badly if done incorrectly, and many people will criticise the inability for many of the new generation to attend university.