When I had 8.1 installed on my laptop I'd gone to blackviper.com and disabled, for the most part, all the "safe" processes. I never even got the Win 10 offer until I restored my laptop OS so evidently one of those processes was stopping the Win 10 offer. Might be worth some testing to determine which one it is.
That said so far I'm pretty happy with Win 10. I went to the privacy settings and turned everything off and recheck them after updates but no issues so far.