Once this information circulates for a bit there's a good chance Bay will respond with an explanation. Stay tuned.
Mark Wahlberg from last night's Tonight Show:
We’re doing a complete reboot of the Transformers. I did a movie with Michael Bay called Pain and Gain, which comes out in April. And we had an amazing time together and really hit it off
Michael Bay from Jack Reynor's Casting Announcement (01/08/13):
Transformers 4, is not a reboot. That word has been floating around on the net.
This movie takes place exactly 4 years after the war in Chicago. The story makes a very natural transition, and reason as to why we have a whole new cast. This Transformers will feel very different then the last three. We are embarking on a new trilogy.
If you would like to watch the interview for yourself it can be found by clicking here.