What kind of a return would you want the upside to be for you to walk out right now and gamble 3 months of salary on a 25% chance of winning bet. Unless you've got significant wealth already then most measurements that take into account the diminishing returns of wealth will probably suggest a that you'll want the win to be at least 6 times that mount.
That's quite a lot of cash for a startup and it makes no sense to a startup that's worried about cashflow to make that kind of an offer when they could give out nice free equity.
Liabilities are much worse on a balance sheet than having employees with stock. Employees with stock in the company have an ongoing alignment with the company; employees who are owed cash are going to be slowly getting more irritated.