Again that is what the Blob does, takes over.
There is no central Mycus no brain, no hive mind, you could maybe apply that logic to the Triffids, because they do actively attack things, but they are not really trying to spread by infecting things, the blob is a sentient mass, that is trying to spread.
The Mycus is just a type of plant, doing plant things, the spores spread the infection, not them attacking/abducting people/creatures to infect.