Did some digging about tax brackets over time and it was pretty eye opening. Taxfoundation.org was a great resource. Just in my lifetime (41 years, which could conceivably be the length of a retirement) tax bracket rules have been set, and changed, by the revenue act of 1978, economic recovery tax act of 1981, tax equity and fiscal responsibility act of 1982, tax reform act of 1984, tax reform act of 1986, omnibus budget reconciliation act of 1990, OBRA of 1993, economic growth and tax relief reconciliation act of 2001, jobs and growth tax relief act of 2003, American taxpayer relief act of 2012, and the tax cuts and jobs act of 2017.
As an example a married couple filing jointly with a taxable income of $50k would today be in a 12% top bracket. 5 years ago they would have been in a 15%. 20 years ago would have been in 27%, and the year before that 27.5%, and the year before that 28%. 35 years ago that would have been a 35% bracket, and the year before that 38%. 39 years ago would have been a whopping 40%, and the year prior even higher at 44%, and the year before even higher at 49%! I understand that most of why that is is inflation ($50k 40 years ago was much more than $50k today).