Interesting question indeed.
If you were working for a mega-corp, then they have very set rules for increasing pay.
For instance, I am allowed to evaluate a new hire every 11 months for a pay increase up to 10%. The 10% is actually a pipe dream, as 5% is all HR would agree on unless there was a severe shortage of talent (like during Y2K).
For more senior people, the timeframe to evaluate is much longer, a person with 20 years experience would be eligible for evaluation every 18-23 months!
This is because they want to move the new hires up in the pay range quicker, since they usually are at the bottom of their pay range. While someone with 20 years would be at the high end of their pay range, and have less room to advance.
So, the bottom line is that if you were working in my company, then I couldn't give you a raise unless it was your "time" regardless of how much I wanted to. Be thankful you have more latitude than I or the people in my company.