It sounds like his pay as a "professor, post-tenure" was reduced to 49% of what it was before, so it's almost certainly a money problem.
Not mentioned yet is the change from defined benefit pensions. If you had a final-salary pension, then there was no financial incentive not to go emeritus, in the good old days. Whereas on a defined-contribution scheme, retiring a year earlier does literally cost you (or your estate) a year's salary.