I'm not sure I understand your question. Capitalism is fairly recent. In fact "businesses" are fairly recent. Humanity didn't idle until someone came up with the idea of corporations, so I don't think you're asking how production or innovation can happen under models compatible with Marxism without reforming existing companies.

Under capitalism, the incentives for new worker coops are the same as for working for an existing company, i.e. not starving to death (or avoiding poverty). Capitalism aside, humans have many incentives for productive work. Research actually shows that intrinsic motivation can greatly exceed extrinsic motivation (e.g. being paid) but adding the latter can almost entirely eliminate the former, chronically: introducing money makes it a transaction rather than a favor.

If your question is why anyone would found a new fruit juice company under Marxist philosophy to compete with the existing reformed ex-capitalist fruit juice companies and claim some of their market share, I think you're still thinking in capitalism.

I also am not very familiar with Marxism so all I can tell you is that humans, generally, are driven by many things and not just by profit.