There are plenty of open source compilers that I can copy and paste whatever I need to. I don't get why you think this would have any level of difficulty?
Of course I couldn't make a brand new compiler that was better than what's out there...
Just like a game engine, I could clone one of the thousands of engines out there pretty easily - making something better or novel would be difficult. Just making a bare bones clone of what already exists by referencing documentation and pre-existing code is relatively easy now.
Yeah, when I made a mediocre 3d game engine 20 years ago, it was brain breaking difficult work. I can make one infinitely better in a micro fraction of the time now because most of the hard stuff is done and can just be looked up now.
Do you not agree?