The aspect of money should not be forgotten, but neither should this simple fact: They only make one main series Pokémon game every year, tops. One every 18 months (with longer gaps between generations) was the norm for a while, but since BW2 things have sped up quite a bit. Time will tell if the new schedule will stay or not.
That means that GameFreak get one annual money boost into their coffers. Okay, the income will be spread out a little, but generally we're talking about one big revenue-collecting sales item per year or longer. Spin-off games certainly bring in some money too, but the big figures are all connected to the main series games. Since the differences between paired versions are minuscule, they should be seen as one game rather than two. Sorry to say.
This rather long period between games means that GameFreak need to make each game as sale-worthy as possible. They have to make the game they predict will sell the best. Otherwise, potential is lost, sales don't go well, and less money comes in to pay the bills. Cue a one-year waiting period before the next big seller can be attempted. Yes, every Pokémon game would probably sell like hotcakes, but it shouldn't be overlooked that some games would sell better than others, and it is in GameFreak's best interest to make the best sellers rather than sticking to a pattern.
To get the best shot at earning their money with that one annual game, they will usually consider several options for what that game looks like. Will it be a remake? A sequel? An entirely new generation? Different games have slightly different target groups, different implications for marketing (which the Anime must be seen as a part of, like it or not), and different projected sales numbers. Remakes will cater to the fans who played the original games many years ago. Entirely new generations means heavy marketing to capture those who have never played a Pokémon game before. Sequels à la BW2 are mostly targetted towards those who bought the games the sequels were based on, in the vein of "If you liked the previous game, check out these new upgrades!" And so on and so forth. The decisions are mostly taken a while in advance, and I expect each generation to be planned out before the middle of the previous one. In other words, what games are going to be made for Gen. VII are probably scheduled already, complete with approximate release dates.
Anyway, this means that a remake is only one of the options to be considered. As I said above, a major target group for those will be players who played and enjoyed the original games, and who still are of the age with plenty of time for Pokémon playing (pre-college or pre-marriage for most people, I guess. Smogon has exceptions all over, but probably doesn't represent an average of the gamer population). I mean, the people who played the original Red and Blue are in their late twenties now, and selling them Kanto remakes again probably wouldn't work that well. Rather, the current target group for Pokémon mostly consists of people who were introduced to the series by RSE or later.
This means that in a few years' time, the "nostalgia crowd" for D/P will largely outgrow the series. Of course, the hard core (like us) will remain, but in the general mix of Pokémon's target group, they will probably be a minority. In other words, there are only a few more years that D/P remakes would be feasible to sell, before the alternatives would be a better choice for the relevant "game release slots" (given the short time span of Gen. V, this will probably arise as a problem if or when remakes of those games will be considered).
So GameFreak might find that while a D/P remake would be projected to haul in big money, maybe a sequel or new generation of sorts would haul in even more. If so, they would be better off dropping the remake, and use their annual main series release on the better option.
Hardware should also be taken into consideration. When the series migrates to a new console, a large percentage of players will probably abandon it. It's easier to buy the games if you already have taken the cost of the console, so when the new game requires you to shell out bucks by the hundreds if you want to play, many decide to save the money and not buy the games. Remember the "outrage" when it was revealed that XY would be 3DS exclusive?
Few people buy a 3DS only to play Pokémon, but many people buy Pokémon because they have a 3DS already. Instead of catering to the former crowd, GameFreak might as well roll out a new generation, targetting newcomers who are willing to shell out for the new console/already have it for other reasons. GameFreak doesn't start a console generation (and by extent, a Pokémon generation) with a remake or a sequel, they cut straight for an entirely new game. This "forces" a slot that might otherwise have been the prime time for releasing a remake, for instance - hence why we didn't get RSE remakes in Gen. V.
So, all in all (TL;DR), the money aspect doesn't dictate that GameFreak should make a game because it would earn money. It says that for an optimal amount of money to be made, the optimal choice of game should be made too. This means that remakes aren't inevitable, since they will not be relevant forever, and there could be other games with potential to make more money with less risk.
That being said, Diamond and Pearl are the best-selling Pokémon games to date, which translates into a very big "nostalgia crowd". While remakes aren't guaranteed, there amount of previous players makes a pretty solid case for it.
