Exactly. Just like buying a car or any other good, engine manufacturers offer ongoing service that can be purchased for future repairs or maintenance. Everything from an extended length warranty, service agreements, parts, engine monitoring etc. If you want more protection, you pay more. Apparently Spirit didn't purchase any of these, or not enough to cover the engines being down. This settlement gives a discount to the tune of $150M for all those repairs, inspections etc but anything extra they have to pay for. This also doesn't include lost revenue, which Spirit apparently doesn't have lost revenue insurance.

I'm guessing that to keep costs down, Spirit just didn't buy anything and rolled the dice on everything working perfectly, which didn't happen and so these are the consequences. Spirit also gives up their right to sue with this, which Pratt's legal counsel or even whoever Pratt gets its Errors and Omissions from might have told them to settle if they want to continue to be insured. Corporate insurance is a huge business, and companies like AIG and Lloyd's of London insure many large companies all over the world. Boeing and GE are largely insured by AIG for example.