That was noted last year at http://www.techrepublic.com/article/microsoft-drops-the-ball-access-2016-not-included-in-office-365/ and other sites.
But don't fret, as an Access developer you could deploy a standalone version. I know many that used a Visual Studio app to provide a frontend to the database. This is far cheaper than Access and gives you a way to move to MySQL for the database (even cheaper.)
After pushing for budget in our company to get onto office 365, I'm left with egg on my face after Access was dropped with no notice to me. So after developing a few databases to better manage some processes, as of last week, we cannot use them anymore.
In as far as I can see, this is a broken promise and apart from feeling like a total idiot for trusting Microsoft now, in this economy, what is with gradually removing features and charging more. In English when you are vested in something and someone takes advantage of that, I think they call it extortion.
Its funny that all the products now on the plan have open source alternatives which means nothing special about Microsoft for business now. I guess we can now call me a Microsoft fool.