Vets are increasingly under pressure to perform procedures for less and less money while trying to keep themselves and their staff paid and equipment up to date. Somehow the public expect that vets will perform work for free, because they love animals.
If you genuinely can't afford to pay, or borrow the money, vets cannot extend credit and surgery and intensive care might not happen for your pet. Humane euthanasia will of course always be an option to reduce their pain and suffering but it is a sad choice for both owner and the veterinary staff.
Pet ownership need not be a luxury item, but there has to be a weekly budget per animal allowed for to ensure they can be fed, wormed, vaccinated, groomed and that an insurance policy will offer financial help when illness or accidents happen. Poppy is the first pet I have owned that has her own insurance policy - after the sudden illness that Saffy experienced and resultant costly spell in intensive care, I decided it was important to ME to have this!
Meanwhile, you might like to compare the costs....
RedditPics - Comparing the Costs of Human vs. Animal Health Care.