Because they are going to allocate as much as they can to that service that is actually using those advanced facilities. The stiches patient in the ER is carrying some load for the cardiac surgery suite just not as much as the person who actually has quadruple bypass. Plus that is just part of it. They're also covering uncompensated costs across the whole system

Even if you only have stitches you want the ER to have those machines just in case the doctor looks at your injury and says "wait, this isn't the standard routine thing everybody has we need to get you into the expensive machines". Probably this will never happen - the doctor will always look and see the standard routine things that everybody has and you don't need the rest.

Elective surgeries have fallen in price because many no longer occur in hospitals. In the USA, ERs have to treat everyone regardless of their ability to pay. That's why you see a lot of urgent care.