>>43517723That's still better than just being given a Pokemon. Sure, it'd be cooler to just come across one, like Moltres on Victory Road in RBY or the whole Celebii quest-thing in HGSS, but even a trip to an island has a nice set-up.
You're a trainer, ferried away to a mysterious island, and as you explore forward you come across a legendary standing in your path, and now it's your chance to try and catch it. It's an experience. A small one, but it's an experience. Far better than being told 'Oh, hey! Someone left this for you, it's one of the rarest and most secret legendaries! Enjoy!'
>>43517003They were major events, for the most part, with hype around them to a place you actually had to travel to; plus there wasn't any alternative you could do. Mew was put into the game incredibly last minute with certain staff not even knowing he was implemented, so it's not like they could put more code in your game that wasn't already there. They're just trading you a Pokemon that's already in the data.
The fact that there was a secret regularly unobtainable Pokemon was a novelty at the time too. It's worn off since then like a lot of other things that were cool in the first few games that have become less cool overtime.
