Inflation erased U.S. income gains last year

"Inflation" simply refers to a rise in general price levels. The cause of inflation is known: someone sets a price.

There isn't a single reason why someone might raise a price. It could be that they have some ideology about the size of the money supply (i.e. "printing money") or it could be that the costs of their inputs went up ("inflation") due to tariffs, or other supply chain problems. Or it could be a cynical bet that the market would bear a higher price ("using inflation as an excuse").

Blaming inflation on this-or-that cause is most definitely a political rather than theoretical exercise.

Why would it be impossible to research it's cause in a specific context?

You are not offering an argument about why can't it be investigated.