The recent Marshmallow has 15.2% market share
Lollipop (14.1% + 21.4%) = 35.5% (the greatest share)
KitKat has 29.2% (the next greatest share)
Jelly Bean† still has (6.0% + 8.3% + 2.4%) = 16.7%
Earlier than Jelly Bean is 3.4% of the total share. Jelly Bean was first unveiled in June 2012, four years ago. I think given the development model: large ecosystem of hardware companies, alternative software stacks like Kindle and Cyanogen, a good chunk of it being open-source; given all that I'll forgive Google that we all can't upgrade to Nougat on the day of its release.As a techie you have to know by now that if you want an up to date version of Android you ought to get a Nexus or a brand which has guaranteed frequent into the future updates. There's not much point in claiming that you're "stuck" at this point.
† Data collected during a 7-day period ending on August 1, 2016.