It was a novel idea at the time because it simulated an adaptive game environment that was so mysterious not even the devs could explain why it existed.
The mystery of Mew is quite literally how this franchise rose to fame, it sold modestly before people started hearing rumors about Mew. If it weren't for this, it never even would have come to the west and Pokemania would have never happened.
Here's the progression:
>Gen 1 it was unintentional but a big hit for the aforementioned reasons
>Gen 2 it was expanded on, with connectivity through the mobile adapter and a neat little event that served to give the "on-disc dlc" more lore
>Gen 3 was the same as Gen 2, but because of the technical incompatibilities, Pokemon that weren't obtainable in RS served as "on-disc DLC" that were little more than a bonus for connecting with other games. The national dex isn't even unlocked unless you trade with FRLG, but at least it's there.
>Gen 4 goes all out with key items that unlock new areas, new lore, and it was all free and done over the internet. Definitely the best implementation of it
>Gen 5 has one key item event with Victini, but the rest are all nothing more than glorified movie ticket bonuses. Stagnation begins here.
>Gen 6 has mythicals that tie into story elements and their influence can be seen in both XY and ORAS with Hoopa Rings. Despite this, none of it is ever explained or expanded on
>Gen 7's first mythical is literally a cancelled Z mon that they shoved in a box
>Gen 7.5's mythicals are even worse movie ticket bonuses
>Gen 8 "mythicals" are a combination of DLC perks and movie ticket bonuses
There's nothing to defend. Back then it was interesting and engaging. Nowadays it's just archaic and other companies provide the same things as complementary or at least give enough of a shit to implement it properly in their games.
