Hi, and thanks for writing. We can absolutely help you with this.
Many factors go into setting a mortgage interest rate. You won't pay the same rate at different mortgage lenders. And different people might get different rates even with the same lender. Just because Freddie Mac says the national average rates are "X" doesn't mean a lender has to offer "X."
See The 10 factors that go into your mortgage rate (and what to do about them) https://themortgagereports.com/31188/how-the-economy-affects-your-mortgage-rate-and-what-to-do-about-it
Lenders may adjust what they charge to control their pipeline. If more loans are coming in than they can process, they might raise rates to slow the tide. If applications slow down, a lender may reduce rates to below market to load its pipeline again. So the reason a specific lender is not giving you the interest rate you want is not the real question.
The real question here is why you are set on using PNC when you can see that other lenders are offering better deals. You have a couple of options. Contact several competing lenders, give them all the same information that PNC has, and see what they offer.
It's easy to get several offers from competing lenders here: https://themortgagereports.com/ratequote
You can choose to work with that lender (who probably deserves your business), or you can try to get PNC to match that offer, if you're already approved and ready to go. They may become more generous if they see that you are not a "captive" borrower.