The following reply is from my own observations, and nothing the developers have said. Sadly, Aground can't be made free. That's not to say it may never happen, Fancy Fish Games has grown a lot since it's initial beta of Aground, back in 2018. Since then they have taken on a pretty big workload, including Aground Zero, which you can view additional information on Steam. If Aground was free, there would be no income to pay rent or the programmers or other overhead costs that make these games possible. This is why my review site always buys the titles we give away, to help support the developers.
Speaking of my review site, were working on a huge server overhaul, and have plans once we're up again on raffling some of the top multiplayer sandbox titles, such as Aground. When this happens, I suggest entering when we do our draws. Only rule my site has, your not allowed to sell the prizes. They must be used on the account that has won them, and activated immediately. Otherwise they do get revoked and never replaced. My site and raffles are not related nor supported by Fancy Fish Games in any way.