Ness, it's just plain more likely that a "blundertale" character would be added than Porky, since "Blundertale" is a 5 year old game, whereas the games in the Mother series are 31 years old (Mother), 26 years old (Earthbound / Mother 2), and 14 years old (Mother 3) respectively, and the Mother series already has two full fighters (Ness from Earthbound/Mother 2, and Lucas from Mother 3) whereas the closest thing to a fighter "Blundertale" has is a Mii Gunner costume. Both games's creators have been afiliated with Nintendo in the past (Toby Fox has composed for multiple Nintendo games, and the Mother series was created by HAL Laboratories), meaning that the creators of each game don't make one more likely than the other.
Also, you can want a character in without insulting an entire fandom. (Can this fandom learn that with regards to Fire Emblem please.)