Those aren't lost sales. Nobody sane would pay $40 or so for a 20 pages paper. Even if Scihub didn't exist. Publishers know nobody pays that. There are other options free for academic, such as subscriptions universities pay for or inter-library loans. Non-academic clients may try asking somebody who has a subscription access for a given paper (I know I did provide paper PDFs a few times when asked). Publishers don't…
My roommate is a student with full access to basically all journals. Funny enough, he still uses scihub because it is easier to use.
At MIT, a few years after the arrest of Aaron Swartz, a prominent researcher from Mass General Hospital was threatened one afternoon with arrest by an MIT police officer for the alleged "crime" of using one of the library computer terminals for "longer than an hour."
It's worth remembering then that there are some out there who are using SciHub now because they don't want to go to jail for trying to access the same content through more "legally legit" channels.