I think I can understand and relate to what you're saying.
I can mention two reasons for this.
One is that there is a black market price and an official price. Like most things, the black market price is higher than the official price. So that is why the rates of banks and other financial institutions are relatively lower than those of crypto and exchanges.
The second point I have is that banks actually buy it from you, so they need a price where they can sell and make profit, while in P2P, you are simply exchanging, so they don't need to lower the rates.
I don't know if it's like that in every country, but if you walk into most banks in my country, you'll see a digital board that shows how much they buy foreign currencies and how much they sell it.
You can see something like:
We buy
$1-150
£1-200
We sell
$1- 155
£1- 205
So you see that the buying rate and the selling rate are different.