Why non-Lumia/non-Microsoft phones do not update to win 10 after more than 1 year?

I have a Prestigio phone, with Win 8.1. I'm waiting for 1 year the win 10 update (last promise was for march 2016). It is unacceptable to say: buy a new phone!

1. The 10 Update was Opt-In so even if it was available you'd still be waiting until you installed the Upgrade Advisor app.

2. Many Windows Phone 8.1 devices did not get 10, much to the chagrin of many, and that likely includes you.