I, personally, don't have a strong opinion one way or another. Yea, it's kind of annoying, but I really don't care. It's what sells the most. The more they see a specific Pokemon get popular, the more they'll tailor to that Pokemon.
Charizard and Mewtwo have a lot going for it. Two Mega Evolutions for each, the two Pokemon appearing in many box arts of different games as their mascots, and Charizard getting a Gigantamax form... It really is no surprise that the two more popular Pokemon were Gen I Pokemon. I mean, the reason why they are the most popular is because they are literally on everything, either by themselves or with Pikachu. It has been like that for years, especially when people start raving how awesome Mewtwo and Charizard were in Gen I and II. The next generation paved the way to make the two even cooler with one of them appearing in a really cool team from Mystery Dungeon Red/Blue Rescue Team.
It's been psychologically tested that the more you see something, usually it grows on you and you start to like it. Though, this usually has the opposite effect, as well. However, the positions of power the two Pokemon have been seen with in the anime and, subjectively (except for Mewtwo as that is not subjective at all) in the games, shows how badass they are. It is one of the reasons why people like them so much. A lizard with wings that breathes fire and an uber powerful genetic monster of a Pokemon who was used for evil now resides peacefully within a cave to get away from civilization? Yea, that's really dope, people will buy that, especially kids, who are the target audience.
I love both Pokemon, with the two being my favorites solely because I had watched the first and second generations of the anime and the First Movie and they had made an amazing role in the entirety of the series. I absolutely loved it. Psychologically, they were amazing. The amount of power they held gave me the want to wish fulfill my way into a deep fantasy realm within my brain to get away from reality. It's an escape and the more impressive they seem to be, the harder the wish fulfilling fantasy sucks you in.
Of course, when you get older your viewpoint tends to change, especially when you want to see your new favorites get the spotlight and they have been denied of this luxury. This usually leaves others to resent the company. I don't resent the company for this reason, as this is all a marketing stunt - a way to cash in on the super popular Pokemon everyone had heard of and known about. If they tried to showcase a Pokemon that nobody has heard before in marketing, it won't work as well and it wouldn't sell as hard compared to slapping a Pikachu, Eevee, Charizard, or Mewtwo with the merch.
Of course, they'll always sell other merch of other Pokemon, but the spotlight will always be at the Pikachu or Eevee or whatever popular Pokemon because that is how they sell more of the merch. A Chingling when Gen IV came out won't sell unless a Pikachu was next to it. This is also for parents who have likely not seen the Pokemon aside from the more popular ones like Pikachu or Charizard. Seeing the two creatures is a lot easier to see that the section in a store is for Pokemon, the thing their kid likes.
Like I said before, I don't have an opinion on the major attention the company gives and their marketing decision is ingenious and I don't fault them for using the cheap way to get more money. However, the spotlight tends to stick and we may get more and more versions of a certain Pokemon that may not be necessary. But it still works. It still hooks the younger audience, no matter what the veteran's views of this practice may be. I don't particularly like it, but it's effective. I love Charizard and Mewtwo and I still do. Though, I wished the spotlight shifted over to other Pokemon, like Dunsparce or Flygon, or the more forgettable Pokemon like Maractus.
Wow, this was way longer than I wanted it to be. XD whoops.
Also, the colors yellow, orange, and red are big striking colors that attract the person's attention. Food companies use this to catch people's attention. The combination of the two colors incite hunger (red) and happiness (yellow). The Pikachu is yellow, so it incites happiness especially to kids who are more susceptible to this subliminal messaging (unless they absolutely abhor the color yellow. XD)
Charmander looks adorable and some chose it because it looked really cute. While Bulbasaur and Squirtle are cute in their own right, Venusaur loses it's cute charm while Blastoise just looks like a badass turtle with cannons. However, dragons have always been a favorite among children and that's partially the reason why Charmander was chosen. Because Charmander was chosen for this reason, people had another reason to avoid Bulbasaur and to choose Squirtle instead.
But anyway, there. My two cents since I have been dying to say this for weeks and I have been waiting till the right time to say something.
