Why are hammerings becoming more common at the top level?

That's not the only reason, although the fullback point is a fair one. This was seen in the Bayern vs Barca games, Robben and Muller raiding Alba. There's also the game in my sig if you want to see suspect defending from fullbacks with little protection from the DMs. The fullbacks being praised nowadays and the defenders being praised nowadays are because of their ball playing ability, not their defending. Luiz, Kompany, Ramos, Pique are seen as some of the worlds best CBs who regularly make errors.

You like the 4-3-3 as much as I do though. But this is a fair point, not the only reason but definitely a reason.

haha of course there is more to it but i like ranting I promise I will stop ranting about the 4-2-3-1 soon. Just after I drop by the Arsenal thread and tell them they should drop Ozil, buy an actual DM, and start playing 4-3-3 to get the best out of Ramsey, Wilshere and Ox.