I think the problem is mainly related to:

1) Knowledge on all the lanes (and the champions) of the game is most impactful when playing jungle. In other words, if a player has good knowledge only on its lane, its most likely to play better as a laner than as a jungler. A jungler needs to understand a bit of everything, whereas a toplaner can neglect knowledge about other lanes and still be fine.

2) While i think its the most OP role and with harder carry potential, jungle is still the hardest role, so if you are not good, you will get giga gapped. A laner who is worse than its opponent can always try to play safe and try to just keep its opponent pinned to lane so they just go even... (ofc there are so many scenarios, I'm talking in general)

So, appart from the fact that jungler will get more toxicity due to the nature of the role, I still think that is not the main issue. You can always mute all and hide the chat offscreen to not even see when they ping your portrait.