Because the companies making the laptop recommend you to shutdown the laptop before puttint it into your backpack.
[1] - https://www.dell.com/community/en/conversations/xps/faq-mode...
EDIT: Added source cited in the article
[1] - https://www.dell.com/community/en/conversations/xps/faq-mode...
EDIT: Added source cited in the article
I do. I had a few poor experiences with laptops accidentally turning on while in the bag between 1995 and 2010.
After the last time, in 2010, when the thing started beeping due to overheating, I started the habit of shutting down/hibernating completely instead of just closing the lid and popping it into the bag.
What an awful laptop.
Don't conclude from your own carelessness to others. Even just one person shutting down their laptop will instantly disprove your claim, that "nobody does XYZ". So you will basically almost always be wrong with such a statement/claim.