The do have competition. It only looks like they don't because they've been working so hard to consistently beat them. There was a time when AMD leapfrogged them and taught them what happens when they moved slowly. AMD had better chips for a good while, there. Intel had to scramble to catch back up, then pass AMD. Now Intel stays ahead of them, always. They improve because they have competition.
And if they hadn't been improving consistently, ARM would be currently eating their lunch in the server market. Which it's not.