Sure there are people that want to farm. But are there people that want to want to deal with sewage? Why do you think plumbers earn more money than other trades?
I want to run a cafe instead of what I'm doing right now. I don't want to be a waiter of wash dishes or anything like that. I just want to design the menus and decide on how it's decorated. Is that the job I'll have in a socialist utopia, or will I have to do a job I don't want to do? What if there's already too many cafes, or not enough people that want to be waiters or was dishes? I won't have to do anything but I'll still be provided for?
In the end there will always be people doing jobs they don't particularly want to do. Someone's gotta unclog the sewage when the elite of the socialist society plug the pipes with the overabundance of shit they spew out.