That's because the MCU draws heavily from the "Ultimate" line of reboot/alternate universe comics that Marvel had running for 10 or 12 years. For example the current MCU Peter Parker is the Ultimate Peter PArker. Still a teenage High Schooler. Movie Hawkeye is Ultimate Hawkeye, a SHIELD Assasin. Not Classic Comic Hawkeye, a Carny. Hulk comes from trying to recreate the Super Soldier Serum. Most of the Super Powers good and bad go back to WW 2 and are offshoots or attempts to recreate Project Rebirth. In 2000 Marvel wanted to create a new easy entry line of their books, that didn't come with all the decades of established baggage. They opted to follow an old design concept from their failed 80's New Universe line. That of being fully interconnected and a bit more "real world". Everything is connected, everything stems back to certain key events or turning points. Of the main MCU characters Captain America is almost 100% classic comic version, as is Black Panther and more or less Dr. Strange. As said above Hawkeye, Hulk, Spider-Man are pure Ulimates line. Ant-Man, Thor, Iron Man, Falcon and Black Widow are sort of hybrids of the two lines with a lot of new.