So that's proof that they can develop and release new game quickly if they want.
Did you purposely ignore everything I just said?
Heart Gold, Soul Silver and Platinum are bigger games that had more new content (Additional areas, redrawn graphics, new music, extra features etc) than Fire Red, Leaf Green and Emerald. FR/LG in particular isn't comparable.
What you say seems interesting. Where do you get your facts from? Im particularly interested the timeline and development process in making pokemon games. Are you able to provide a link to the website you got your information? I would very much like to read it
It's simple when you look at things from a business perspective. There are many, many games that have been shown to have content removed in order to make release deadlines, even what can be called the flagship games for a publisher. Take Sonic The Hedgehog 2, for example. Thanks to the work of people finding
several prototype ROM files of Sonic 2, ranging from
quite early in the games' development to
mere months before release, we've found there were a lot of ideas planned for stages and other features that were simply removed because they couldn't fit them in. This is backed up with official statements from people who worked on the game that they had to abandon some concepts that couldn't be implemented for Sonic 2's well-publicised release date. This happened again with Sonic 3 - the two games we see as Sonic 3 and Sonic & Knuckles were originally supposed to be a single, massive game.
A lot of high-profile video games will have elements scrapped or stories with missing content because they had to be tied up in time for release.
As for Pokémon, Junichi Masuda once said that
"We spent four years for creating Pokemon Black/White with great care.". From this we can reliably conclude that after Diamond and Pearl came out in 2006, all three games (Platinum, Heart Gold, Black) were in some form of production at the same time until 2008, with Platinum coming out first, Heart Gold in 2009 and Black in 2010.
Since then, who knows what they've been doing although it's obvious at this point that there will be no more Pokémon games on the DS, so we can guess that they've been developing for the 3DS over the past year, like how they took 2 years after Crystal to bring Pokémon onto the GBA, and another 2 years after Emerald for Pokémon to come out on the DS.