Generation defining launch/early games traditionally sell better than their sequels or successors. For Zelda... OoT doubled Majora's Mask's sales, Twilight Princess almost tripled Skyward Sword, and BotW will probably beat TotK by a good margin.
I haven't been paying close attention to Nintendo's software, but Odyssey shrinking the gap with BotW can partly be attributed to TotK cutting BotW's legs.