When it comes to Apple, I believe it was not anticipation, but overreaction to the Galaxy Note. Phablets quickly became popular in East Asia[1], and "pocketability" turned out to be a complete non-issue for the many women who carry around a bag all day. But instead of just serving the phablet market, they've gone all-in on it.
That said, I absolutely agree that companies often converge on weird standards. I'm glad that the glossy screen hype seems to be mostly over, but now we're losing inverted-T arrow keys :(
[1] https://www.theguardian.com/technology/2013/sep/02/phablets-...
They were absolutely nervous about losing sales to larger phones that customers liked. Turns out reaching everything with one thumb isn't really as important as having a big screen to view content on.
We know the rest of the story, the next year the next iPhone became larger...
This is not sufficient reasoning — industries can independently yet collectively decide what the next big thing is, and operate in tandem to produce a market where only that thing exists. Notably, the shift to large phone sizes occurred rapidly, suggesting this may have been the case. That the shift was not a reaction to consumer interest, but rather in anticipation of it.
The biggest recent example of this effect was the 5 years or so where every new tv was a 3D TV; its now been phased out in favor of SmartTVs, which I personally believe are shitty enough to likely have no real consumer support. Another example is car touchscreens, and their somehow consistent terribleness across all brands, even luxury ones.