Hgss, for example, you had to enter the hall of fame, complete the national dex, set records for everything in the pokeathlon, get the leaf crown, and hit a streak of 100 in the battle tower. There was actually a sense of accomplishment when you achieved the difficult criteria. All the different colors you could have for your trainer card was nice as well.

When xy/oras happened I easily completed them because all you needed was to beat the hall of fame, complete the regional dex, and beat the maison leader in 'hardmode.'

I know for a fact in oras you only needed to see all the hoenn pokemon to get the gold card, don't even have to catch them.

Sm just got rid of the card entirely by featuring stamps on your passport; it doesn't even change colors.