Why isn’t my credit score changing

I have a few Capital One credit cards, one from my credit union I’m a part of, and a Credit One card that I’m trying to cancel. I’ve had them all for many years now and I almost always pay my balances off in full. have scheduled payments so I am never late with my payments, I think in the past 7 years I’ve only been late once and my score is still sitting around 715-720 and it hardly ever changes. How can I boost it up? When I apply for more credit cards it gives me hard inquiries which just drops my score further so I feel like it’s a lose-lose situation and I’m just feeling discouraged now after being so on top of my payments but seeing no benefit