Friction in Cloud Services Contracting

If I can sign up for your cloud service without human interaction, why do you make me contact your billing department to cancel or downgrade my subscription? 

This question came to mind after an experience I had this week dealing with a well-known SaaS provider this week. The provider, who will remain unnamed, is well-known in the market for "collaboration."

Although this provider serves many large companies, it is also a good choice for small work groups, which is how my consulting firm is using this service. There is a free trial version, which will convert to a paid subscription for a nominal per-user fee. As such, without interacting with a human being, you can sign up for a handful of users for an entry level service.

The experience this week started when our annual billing notice came in and I realized that we were paying for a level of service that was much greater than what we need.  So, I looked at the provider's website to see how to downgrade our level of service.

The instructions I found read, in effect, "Contact our billing department."

Now, to the provider's credit, the billing department handled my request in a fairly efficient matter, although of course they wanted to know why I wanted to downgrade, had they done anything wrong, did I realize all the benefits I was receiving, etc., etc. I believe I needed to respond to two, perhaps three, emails in order to accomplish the downgrade.

So the question remains: Why require this extra step?  If I can sign up via self-service, why can't I downgrade or cancel via self-service?