How does one expect to build a tractor without materials? Like a mine to get iron ore from the ground, foundries to smelt it, machine shops to craft parts, rubber or oil processing to make tires, etc.? Supply chains under a command economy have been much worse slavery just as much as you would say they are when people are paid for their labor.

Let's look at examples. Albania's socialism was incredibly closed off, and the Hoxha regime a full on analogue surveillance state because they didn't trust their neighbors because they weren't socialist enough. They bought tractors from other socialist countries for decades (socialists doing capitalism with the government, so it doesn't count), until in 1978 they finally just made a factory to copy the Chinese tractors they were buying because of their paranoia about other socialist countries trying to infiltrate them.

Of course I'm describing capitalism, because I'm telling you that you genuinely can't expect some noble socialist utopia to actually get you tractors without conscripting people who don't want to build tractors into receiving rations - or money, take your pick - to work in a factory.