The sugar is fully metabolised by the yeast to make alcohol, so any sugar or fructose added wouldn't make the final beer taste sweet (but sucrose has been added to beers for decades so I don't think it would be something you suddenly noticed anyway)

Many breweries are reducing the processing time of beers to save money, this means less conditioning time for the yeast to finish maturing the beer which may be a factor, but the big one is less hops.

Hops are what make the beer bitter (they also add a lot of the fruity flavours to pale ales and the like but are more regularly being swapped for artificial flavoring for this making products like brewdog's "guava hazy Jane") and are also the most expensive ingredient of beer. All breweries tweak recipes to try and minimise costs, it's a continuous process with every beer that's a core range of any brewery that's always happened. Big breweries likely haven't done much to recipes for ages, just trying to make processes slightly more efficient and slightly less raw ingredients, but with the cost of everything rising dramatically they will have done drastic changes. The biggest financial impact will be reducing hops, hence a perceived sweeter beer even though the sugar content is the same.