A few ideas on why reducing profit by investing into the company might not be their best choice without the new investment round:
Hiring people is hard, takes time, and timing of big sales closing causing income may not line up well enough with the hiring process to offset that income fully.
Their machines are sold for high prices. It’s not small and not cheap. If a buyer pays in a lump sum that can be a big income and Oxide may not be able to time that ideally for tax purposes.
Buying electronics components is funny. Want to buy 1000 units? Price X. Want to buy 100,000 units, price is X/25. But till you can place an order for every component at the 100,000 quantity, you can’t get those price breaks so your cost to manufacture machines is much higher. $400M may let them buy at those bigger quantities and get those price breaks and it may not have been worthwhile to buy inventory at the lower quantity pricing if the investment round was looking to close real soon now. Cash flow is king, and hard, for hardware companies.