I just don't understand the logic

I was in a supermarket yesterday.
I saw a packet of Scottish shortbread biscuits.
Here's the packet with the price for a 175g box (609yen):

Okay.

Then, I saw the price for a much smaller, 2 portioned, 40g packet - 105yen.

See the problem?

Let's look at the big box. 609yen for 175 g. That comes to 348yen per 100g.
Okay, now the small packet. 105yen for 40g. That comes to... ...ummm... 262.5yen per 100g.

???????????????????????????

If you buy 175g worth of small packets, it will cost 459yen - saving 150yen over the box!
Small packets are better - your biscuits remain fresh and sealed.
You may point out that you can't buy a fraction of a packet. So, 4 packets are 160g, costing 420yen. You lose 1/2 a cookie, but you save 189 yen (you can buy another packet of 2 cookies with that and still have money to spare).

Why buy the box?
I don't understand.