You get paid for being a solid addition on a team providing steady progress. If you continue to do the same thing and make the same valuable but incremental progress, why should your job role change?

This is one of the advantages of having reasonably wide pay bands at Google. Doing a great job within your level will earn you raises. You don't need promotion for that (to a limit). Why should promotion just be something earned after doing the same thing for a long time?