Handling further tuition is a really difficult thing to do well, economically. If you make it free, you're taxing people who didn't benefit from it, or only benefited from it indirectly (better doctors, etc.), to give to people who did benefit from it and can expect to get better jobs as a result. It's almost a direct poor -> rich transfer. But make students bear all the costs, and suddenly you've stratified society so that only the rich continue to be rich because they're the only ones who can afford it, and everyone suffers as a result from a less dynamic economy and so on. You need to find some way of doing it so that people get charged roughly in proportion to their expected benefit (or slightly less, given risk aversion), and so that the state gets charged roughly in proportion to the expected benefit of those not taking the degree. But that's nearly impossible, because how many people can accurately assess the benefit of a degree to them personally, and it ends up being even more complicated when less people taking degrees increases the benefit of you having a degree, and you end up with all sorts of coordination problems.
There's some cool economic models that solve the problem, but running them in the real world would be difficult. You have HCC models - human capital contracts - where people essentially get money for their degrees in return for giving up a small portion of their income to whoever gave them the capital. They work because, given your income should vary with how much private benefit your degree gives you, the HCC pays out differently according to how much private benefit your degree gave you, so whether or not an institution pays out to you depends on how much they think you'll benefit from your degree, and they're often in a better position to assess, so it solves the information problem and the co-ordination problem (to an extent) by reducing the number of agents.
But if you make HCCs too fine-grained, you end up with all sorts of weird problems - like, black Americans end up earning less than whites, so their HCCs pay out less. You have to try and make it so the sole differential variable is what degree you do, so legally every institution has to offer exactly the same loan to anyone taking a particular degree, but there are tonnes of universities offering a huge variety of degrees and so that standardization becomes very difficult.
I've seen some people suggesting the best way it would work would be the teaching institutions themselves going to institutions, saying "here is the degree on offer and our teaching methods and so on", the institution saying "okay, we'll offer a deal of x% of your students' income for y of their years after graduation in return for z payment from us to you as an institution", and this is without knowledge of the students, only the university in question and the degree they offer, and then universities publish the sort of HCCs the degree is accompanied by so that students know what the money looks like when they apply, but then you have conflicts of interest where universities might abuse monopoly positions and so on.
Then you start saying "well, let's take it out of the hands of institutions and have HCCs to the government", which is... a tax, on graduates, and then you end up with a whole raft of problems on top of that - like, can this be defended? Because judging most countries where people owe a fee to the government, the issue gets politicized and you have fee creep, like in the United Kingdom, from free -> £3,000 -> £9,000 and now they're talking £12,000; and the government has a big incentive to post hoc underdeliver and universities end up suffocating for budget.
And at this point you just tear up all the policy papers you've read and start crying quietly. It's the ultimate optimization problem: public good, private benefit, imperfect information, information asymmetry, prisoner's dilemma, you name it, education fucks with it.