>>57598118One word: normification.
Think about it: back in the 90s, when Pokémon reached the US, we were all "Wow, a game where I can capture monsters and fight with them! Cool!" The anime was hyping the momentum, and word of mouth made sure this trend would last one or two years.
New consoles and games made sure we had something to latch on:
>Gen 1: the original game>Gen 2: Full color and following Pikachu (if you have Yellow)>Gen 3: a reboot with better graphics, animations, and even 3D games!But here is where Pokémon died as a niche and became the norm: with Gen 4's wifi.
We suddenly had global trades, everyone was playing Pokémon, and even got the best remakes. FRLG was a right step with the Sevii Islands, but with HGSS making gen trading easier, plus having both new children playing and old players grabbing the games due to their memories.
After Gen 5's failed attempt to a second reboot, games just became "remember Kanto?" every new installment. Hell, this is the biggest issue in Gen 8, when they tell you "remember your Pokémon?", but then you can't bring them to Galar due to Dexit.
Everyone knows Pokémon, everyone played at least one game, and even your niche side games are very well known and documented (looking at you Rangers, Gamecube games, and Conquest. And let's not get in the revival of the GBC TC games.)
Pokémon didn't lost popularity, it just become the new normal.