Thomann aren't stupid, the basic models like the PB-20 & JB-20 are perfectly acceptable basses. If they were crap there's the risk folk would just give up,that means no further business. By offering a nice bass for peanuts chances are the learner will stick with it and maybe buy their upgrade from Thomann.
I much preferred the full scale PB-20 to the Squier Affinity P-bass.