Thinking you sound polite, natural and like a proper English speaker. And while these are technically correct, the problem is that no one actually talks like that. Every time you use one of these phrases, you're basically holding up a little sign that says, "I learnt English from a textbook!"
It's not your fault. These phrases are commonly taught in many English courses. But if you want to sound genuinely fluent and natural, today’s lesson is for you!