With the release of War of the Spark, the rules for Proliferate changed. Previously, they allowed you to add 1 counter to the chosen permanents and players, of a type it already had. Now, it adds an additional counter for every type of counter already present.
This seems like a big change that suddenly changes the way a bunch of existing cards work; in most cases making all of those cards stronger. Why alter the power level of all those existing cards? It almost seems like if they one day said that from now on, "Lifelink" means that you get 2 life for every damage instead of 1.
In this article about War of the Spark rules changes, it mentions that the rules were changed:
The rules for proliferate got a makeover! The rule reminding you who chooses counters is dropped, since there are no more choices on the counters, and the other two rules are updated to match the new reality.
But this seems to be a change just to deal with the fact that "Proliferate" changed; it's not an explanation of the fact that Proliferate changed or why.
Is there an article or source that announces and explains this change?