Just because an SMS originates from a computer does not make it spam. I like to be notified that my drive up order is ready or for a link to check in at the doctor.
That's why making each message costly is the way to go - it's not discriminating on what or how sent the message, it just forces sending to scale no faster than actual service of the business. A text or two per delivery or a doctors' visit is still a rounding error compared to costs of the transaction itself, but casually spamming hundreds of thousands of people becomes a noticeable cost.
