Strange decision to force private users to upgrade

It was always a great thing to use TeamViewer for free as a private person to support another private person once in a while. I have a typical use case here, I'm a daughter supporting her mother with an older iMac in another part of the country.

So now, as I understand, these times are over :-(

I cannot understand why TeamViewer now forces private users with the free version to upgrade to the newest version. We both have TeamViewer 12 which should run on my iMac with Sierra and her iMac with Mavericks. But it doesn't. My mother cannot upgrade to version 14 because her iMac still runs Mavericks and we cannot take the risks of upgrading her older iMac at the moment. A commercial license is way to expensive for a private person having to do support maybe twice a year.

I cannot understand this measure, mainly because I guess this is very often the case for private users that they have to support older devices of their family members. 

It makes me very sad :-(