Why do assets like purchases, expenses, vehicles etc posted on the credit side of an account?

Pay no attention to what makes sense. Its a simple matter of which side they go on.

I would have thought that Never, thanks. It's just that I read something in a book that confused me.

Are you talking about your credit account? Because these would be items you have gotten a loan for or used credit to buy. Purchases and expenses are NOT assets, and neither is a vehicle unless it is paid off. They are all debt.