1. Salary will plateau eventually. I know early in your career it doesn't seem like it will, but trust me: It will. I don't care what company you are in, or how good you are, "Fourth Senior Software Engineer From The Left" is never going to be making $1M/yr. (Not that that should necessarily be your goal, but it illustrates that you will plateau at some point.)
2. When you keep job hopping for more money but no change in level, you risk gaining "1 year of experience 20 times" instead of 20 years of experience. You're sacrificing long term career growth for short term salary bumps. I did this for years and ended up shooting myself in the foot long-term. My college friends, who instead played the Title / Ladder Climbing game, are all much better off than I now. They're all job-secure VPs, SVPs, and CxO's in their companies vs. me who still doesn't even have any direct reports, and is one of many interchangeable worker bees.
No more doing that for me. I'll only accept, at a minimum, a level jump at this point.