Part of it is that there's less hidden costs. I like it when it's just "the total is $30" instead of "there's $8 shipping and a $2 service fee and then $4 in taxes and..."

I've also seen some online stores lure in a customer with a really cheap initial price and then on the last page just slam them with insane shipping and handling fees hoping that the customer either doesn't notice or feels too invested at this point to cancel their purchase.

But yes, part of it is also people are stupid when they see the word "free" as if the store wouldn't move the cost somewhere else.