The basic idea of shared means is that if you let someone privately own the means you deprive everyone else of that resource, unless you pay them to use the means, and then you are back to private ownership.

You are also creating an incentive not to share your tilling machine freely, because you're now in debt and if you let your neighbors use it for free, why is that fair if you paid for it? Might as well charge them for it, and if youre smart you start lobbying against the others buying a communal machine, because then nobody would pay to loan out yours any more.

Instead the tilling machine is paid for by all local farmers together, meaning nobody has to go in debt or pay for using it. Who gets to use it and when is just a matter of scheduling, and if wait times are too long you buy another together.