I don't think it's the SOFTWARE upgrade they're after
Alongside the Win 10 upgrade appears to float a fairly substantial change in Terms & Conditions which switches users from "I paid for it once, now go away" to "you owe use an annual tithe for this use or we'll blackmail you with your own data" model.
I suspect this is really the main reason for the pushiness: hard, cold cash.
Win 7/8 gave them a one-off hit of their favourite addiction (money), Win 10 gives them returning revenue, and I am willing to bet a substantial amount of money that that charge will go up substantially the moment they feel they have enough people locked in - inertia wins every time.
It's a good strategy from the perspective of a persistent abuser: nice bit of data you have on your computer and in our cloud, it would be a shame if you couldn't get to it anymore. I guess they learned something about viruses after all, just not anything that helps the *user*.
Windows now truly has become the virus we used to joke about. Bail while you still can.