Mining Cryptocurrency Is Against CenturyLink's Acceptable Use Policy

I was reading through CenturyLink's Terms of Service earlier tonight, and stumbled upon their Acceptable Use Policy: http://www.centurylink.com/aboutus/legal/acceptable-use-policy.html

I was quite surprised to read this particular section:

Users will not use the Service (a) by any means or device to avoid payment; (b) to access User’s account or CenturyLink Services after User has terminated User’s account; (c) on behalf of persons or firms listed in the Spamhaus Register of Known Spam Operations database at www.spamhaus.org; (d) to engage in phishing activities and (e) for purposes of cryptography or similar computational processing to mine or create units of cryptocurrency, such as Bitcoin, Ethereum, Ripple, and Litecoin.

Is this becoming a norm for ISP's? Does anyone know why they would have such a policy?