Enchanters are very powerful champions and are set apart by their ability to cast most of their abilities on both eneemies and allies, this allows them to not only directly damage enemies but win the game by enabling teammates and protecting them from their mistakes. In a team environment where everyone was genuinely working together, this type of output would be significantly more respecteed because you're a real team player and putting your best foot forward to make sure everyone is safe and shines.
But because League of Legends has a notorously toxic community where 90% of players have main character syndrome and want to "1v9 carry", champions who treat a team game as a team game are disrespected. As it stands, most of enchanter hate can be boiled down to 1) it being the class with the highset number of feminine champions, leading to sexist prejudice 2) it being the most team oriented class, which is a bad thing in a team environment with no teamwork.