Why do they reference the old games so much when the new ones are nothing like the first?

I have played almost every game in the following order, I have played Diamond, Pearl, Heartgold, Soulsilver, FireRed? Y and Ruby twice through,

Diamond (2008)
Platinum (09)
Soulsilver (10)
Heartgold (11)
Black (11)
White (12)
Black 2 (13)
White 2 (14)
FireRed (14)
Ruby (15)
Emerald (16)
Y (16)
Sun (16)
Alpha Sapphire (16)
Ultra Sun (17)
Ultra Moon (18)
Shield and DLC (20)
Brilliant Diamond (22)
Legends Arceus (22)
Scarlet (22)
Scarlet DLC (23)
Legends ZA and DLC (25)