Quality control. From reviews of such knives, the heat treatment can be not so good.
Geometry.
These knives are often a flat slab of steel with an edge. From the photo of the knife you linked, the top 2/3 of the blade is uniformly thick, and the grind begins below that. The spine is uniformly thick from the handle to the tip. These things are common enough - standard on cheap stamped knives. However, these knives often have thicker blades than the average cheap stamped knife, and this can make the knife heavier and thicker-tipped than it should be.
Also, don't believe all of the advertising. The knife you linked claims 62+ HRC; they are probably quoting the as-quenched hardness, rather than the actual hardness.
They can be OK for the right price. There are much worse knives out there. For about the same price, you could buy this beautiful knife, 420J2, barely over 50HRC:
(of course, this knife is not recommended in the wiki).