How could gamefreak make you want to catch all pokemon again?

my idea would be

you catch 50 pokemon> you can now travel the land to catch the legendary birds
if you cought them a cave opens in order to catch lugia
same with legendari dogs

you cought 150
now you can travel to faraway island in order to catch mew

and when you cought all but one pokemon you are aloud to catch arceus

and sometimes nintendo makes a wifi event where you could get certain pokemon for free

also who here has cought all pokemon?
and why