Why didn't you just take your Mazda to the local honest mechanic who does everything quickly, too? There's nothing different about routine maintenance such as oil changes and filters.
Do you mean to ask why did we get the prepaid plan at all? It was discounted significantly (because I said NO) but they did not tell us it is not the comprehensive plan they showed us before.
Or do you mean to ask why did we go to Oak-Tree at all after getting the plan? We assumed it is a comprehensive plan and we already paid for it. Going to the mechanic means we pay extra, especially for routine maintenance. We are a captured audience. On top of that, for warranty work we'd go to the dealership regardless.