Here's a theory on the siping:
If they had full-depth siping, those tires would CHUNK! You'd have pretty tall, thin slivers of unsupported rubber. It wouldn't be pretty. Would probably have about 10x worse responsiveness than that kind of tire already has. "Tread squirm", they call it.
So... if you put a new set of cheap "snow tires" like that on the car at the beginning of winter... maybe by late spring the siping will be gone. But, so will the snow! You'll be good through the spring rainy season. If you're doing it right (driving it like you stole it), you'll be at competition depth by summer. And then you'll be ready for a fresh set at the beginning of the next winter!
What? Y'all don't buy tires every year? (I'm an autocrosser, I tend to buy a set of tires every 8-11 months on average)