Were the duration of Bachelor's, Master's and PhD degrees different in the U.S. 100 years ago?
In the U.S., the Ph.D. is longer now on average, especially in the sciences because of the influx of money for paid research, the use of grad students to do research, professors as almost pure managers and grant funders versus real working scientists, etc. It has become something like Renaissance painting done by subordinates.  Except I still think the painters got their hands dirty and gave instruction.
There is almost no apprenticeship in R1 science from the professor, just other students and perhaps post docs. It is essentially about milking the grad student for results to get more grants, travel, promotions, grow the empire, etc.  Thus the expectation for work product has gone up.  Add onto that, that the money has enabled way more actual Ph.D.s to exist, but not increased the number of geniuses in the population and fundamental advances are if anything harder as simple much of the low hanging fruit is plucked.  And you have a situation of volume of result being emphasized.  Not the trainee education.
And enjoy the job market at the end...
All that said, if you sniff around you can find profs or even departments that still emphasize the classic 4 years.  But you will have to search. It is abnormal now.