Why does my IPv6 address change more often than my IPv4 address?

I'm a bit peeved right now at Cox.

I'm trying to do an IPv6 IoT project for some devices (using ipsec), but it's difficult because my IPv6 address and prefix are constantly changing. My IPv4 address doesn't change though. This is ironic.

Isn't this the exact problem that IPv6 was supposed to solve? What's the point in changing the IPv6 address and prefix all the time?

So I called support asking for a static IPv6 address and prefix. I was told I would need a business account for this (!).

Come on people. It's 2017. IPv6 is happening.

FYI, another family member is using Comcast and their IPv6 address and prefix hasn't changed for at least 6 months. So I'm tunneling one of their subnets from the /60 allocation through a GRE tunnel to my router so the addresses can stay the same while I test this.