Because if you're not pre-approved, it's a waste of time. Your time, my time, the listing agent's time, the seller's time, etc. If you're a serious buyer then you need to get pre-approved first. Just because you think it won't be a problem getting pre-approved, doesn't mean you necessarily will. It takes a lot more than a decent credit score. Lenders are going to look at your income, job history, debt to income ratio, savings, etc. They'll ask for tax returns, pay stubs, and bank statements. Not sure what the market is like in MI, but here in CO we are in a hot seller's market. If you want to be taken seriously, then you need to be prepared and be pre-approved and have a letter in hand.