A significant change in the United States patent system came in 2012 when the Patent Law of 1952 was largely revised to "modernize" the United States Patent Office. This was the enactment of the "America Invents Act".
The major impetus behind a need to "modernize" was that the United States was essentially the only country in the world which granted priority to an inventor if he/she was the first to invent. That is, if a first inventor could show a reduction to practice (such as a working model) before a second inventor, then the first inventor would be awarded the patent even if the second inventor filed a patent application for the same invention before the first inventor.
Modernization was the catch phrase because the rest of the world had gone to a first to file system.
First to file is a bit Draconian (shall I add unfair?), but very simple to administer.
In the first to invent system, a conflict in inventorship had to be decided by a complex, costly and lengthy "Interference". In the first to file system, it makes no difference who invented first; it all hinges on who filed first.
My colleagues and new practitioners appear to have meekly accepted the change. The change, which seems to favor expediency over fairness, bothers me to this day.