. . . Well, to be fair, it seems like most of the current novels now are or will be taking place in this hundred-year gap, so I think they don't want to provide details because (a) the Novels aren't all finished and they don't want to spoil them and (b) there is enough of the "unknown" that they don't want to be tied into a fixed and detail 100-year plot.
I agree with you that this is probably why they don't have the timeline included. Not to argue, just stating fact, there hasn't been a campaign/setting book of FR in any edition, that didn't include a timeline. Now, I would understand them not reprinting timeline entries that are already more fleshed out in
The Grand History of the Realms than they ever were in any other FR product, but not providing a timeline of the last 94 years, when a new campaign might very well be dependent on knowing what happened in those intervening years*, is completely unacceptable to me in a $40 product. I mean, this is
THE Campaign Guide. This is the prime sourcebook for DM'ing the Realms. Now if revealing major timeline occurences would cause spoiler issues with upcoming novels, or even worse, they don't have the timeline fleshed out yet (despite having a bare-bones timeline included in their advertisement), this tells me one of two things: a) they weren't ready to reveal the new realms and don't have the game side in sync with the novel side - or b) they don't have the everyting properly fleshed out yet. I personally doubt it's "b". They could have given a timeline with all of the elements that wouldn't spoil the novels, or written them in a way as to be teasers for the novels. But, in comparison to other edition Campaign/Setting guide releases. This falls way short.
*The beginning of chapter 2 states: "The easiest way to adjust your campaign is to change it all at once. Continue your games events in 1375 DR and beyond if you wish, perhaps using some of the events described in chapter 6 and in
Grand History of the Realms to introduce the "future history" of the setting into your game."
I understand that no-one is making you use FR canon in your game, however, there are those who
want to use FR canon in their game. For those who want to use canon, at best, they are essentially running their games with loose "preview" style information. People running the Realms have already been doing that since the anouncement of 4E. However, this is a $40, supposedly definitive, sourcebook product. Without the timeline information, this product cannot be used as definitively as past edition campaign sourcebook products.
The timeline may not be that important to some, or even most, of the people who would buy this product. But to me, It is a huge hole in the middle of what otherwise is a pretty good product.