On the contrary, you're getting blobbing mixed up with spamming. Spamming is when you make a lot of the same unit regardless of how you use it. Blobbing is when you put a bunch of units into one big mob and move them all around at once with no attention to cover or tactics. Often times they overlap, such as a blob made up of 5 Riflesquads, but not always.
Spam takes more effort to use, because you still need cover and tactics. Spam is often a side-effect of other units being less effective even with combined arms, than simply building one type. It happens because the weakness of building one unit type is still stronger than the weakness of diverting resources to another type.
Blobbing takes little effort or risk for high payout and is popular among low - mid tier players, even moreso with Americans since they can create the most versatile blobs. The biggest blobs (what I call "critical mass") can even steamroll things meant to counter them, like Machine Guns and Tanks.
+1
I think blobbing for all factions needs to be addressed but especially for the U.S where it seems very prevalent.