>>33332004Because, like gen 6, they are each designed purely to appeal to a particular human demographic:
The appeal of the starters in gens 1-5 is that they are a symbol of your strength as a trainer, with their designs being close enough to their inspiration that you can project either gender or character onto them as you wish. They look strong, wise, ready for any battle and you know they'll protect you.
Incineroar looks physically strong and battle-ready, but rather than being a fire-breathing big cat that we ALL wanted and need, is some sort of juvenile high school prick. Its wrestler character dominates its already unnecessarily-human design. Girls love felines no matter male or female, but do they like wrestlers? It also seems to spout fire from near its genitals - I don't think this is a coincidence. It has clearly been designed to appeal to masculine sensibilities.
Primarina is a good classic Pokémon design - don't get me wrong - since its siren character compliments its seal inspiration. However, like Incineroar, it is obnoxiously gendered to the point where it has become a meme as "tranny seal", because transsexuals and drag queens magnify their feminine qualities in order to hide or escape masculinity, and this is what Primarina seems to do, with its pink stars, frills and pearl accessories. But, no man wants to be seen being rescued by a woman.
Decidueye is a good example of a classic starter design in terms of it being close to its inspiration and gender-neutral, but even it doesn't compare to the likes of say Torterra, Infernape, Charizard, Blastoise. It just stands there with its flimsy cloak of feathers and twiggy legs, shooting an arrow from behind the trees because it's too puss to be capable of anything else. Decidueye doesn't like having a trainer, but feels like it should because it needs you to rescue it from its passive attitude to life.
Why are they polarizing? Because they work around opposing poles: masculinity and femininity.
