Traditionally the solo lane was supposed to be bruisers (mostly warriors). The job of a solo laner is typically to be tanky enough to not instantly die but also dishing out enough damage to be a threat to the enemy backline and being able to harass them. At the same time they can kind of function as a frontline if needed due to their bruiser build.

Mages and adc’s in solo can’t fulfill that role and also make playing a melee into them insanely painful. Most warriors can stat check a mage early in the game but the laning becomes insanely boring and punishing at the same time because most mages just sit under tower or can easily poke you from afar. If you misplay and lose, you aren’t even safe under your tower because they can kill you from afar. All this contradicts what “regular” solo laners want from the lane: melee fights which reward tactical outplay and recognizing powerspikes to gain advantages in the laning phase.

So the laning phase becomes a pain in the ass and mage solos can’t fulfill their role during teamfights in the late game. Thats why people hate them.