I am not sure about your situation and laws....but when you look at the national plumbing code (so not the my state rules) there are some requirements where a property must have enough room in the yard or property to have two full size absorption bed or trenches...in case one fails you have room to build a second..so this must happen quite often in some areas.
I think many times it depends on the soil on the property and what was put into the system....so if the septic system failed, it may not have been the tank itself, which could probable be dug up and replaced...but the absorption areas where the fluid goes is what has failed...so now the soil can't take in anymore liquid and properly drain effluent and clean it. It could be that the organisms that usually digest the fluid don't function anymore or maybe the previous owner dumped cooking oil down the drain too many times

Replacing your system may involve installing a larger tank and hauling out the old soil and bringing in new soil or installing a special kind of tank. Around here there are many wells that people install, so if you are within 1000 ft of a public well you need an expensive system installed (or more expense than the standard one). Soil with poor drainage qualities also will increase the size of the absortion area and therefore the expense.