Most salaries reported in Glassdoor are several years old as Zuhayeer said. However, Glassdoor doesn’t even adjust them for inflation. So any statistic based on them will be horribly inaccurate. From personal experience too I can tell you that levels.fyi is far more accurate than Glassdoor.

P.S. I’d also like to thank Zuhayeer for building levels.fyi. It’s an awesome tool and helped me greatly in negotiating.