Opportunity cost is no less real than other kinds of costs. If not for the cost, their bank account would have a higher number in it.
If you have a bank account with $100 in it, a $10 daily expense will deplete your account in 10 days. A $10 daily opportunity cost would never deplete your account.
Well that's assuming you have no expenses. In your example the difference between realizing the opportunity cost or not is the difference between 10 days of runway and paying the bills in perpetuity.
Bills pile up no matter what, so there's only a limited amount of opportunity cost you can afford to eat.