Not sure where you got the idea that the Nexus 5 didn't get Android 6. I still have the Nexus 5 and got Android 6. It was also still getting security updates until December last year [0].

Android 7 was only announced in Match last year too, and wasn't released until August, 5 months later, so it's not even been out for 6 months yet.

Personally, I've switched to LineageOS which is on Android 7.1 and that is working fine (although I understand that installing ROMs isn't going to work for the vast majority of people). With a Google branded phone getting ROM support is more likely to be supported for those that care about it, otherwise 'normal' people will just get a new phone every 1-2 years when their contract is up for renewal.

I don't really agree with this, but 2 years of OS upgrades and 3 years of OS security fixes (from Google for their phones) seems 'okay' and is better than what most other phone manufactures (of Android phones) offer.

[0] https://developers.google.com/android/images#hammerheadm4b30... (6.0.1 (M4B30Z, Dec 2016))