[cratermoon]

Title inflation. I speculate based on no evidence other than my own observations that it's because companies aren't willing to pay entry or junior engineers well enough, so lots of them get hired at lowball rates with an implicit understanding that they'll get promoted to senior after 3 years and get the a corresponding pay raise. Either that, or they don't get promoted or a raise, change jobs, and get the senior title by default.

[manicennui]

Promotion is absolutely my employer's main retention tool. Many of our senior engineers who leave don't end up with a senior title at their new employer, but they do get a bump in pay.