The trouble is that adults who mispronounce words almost certainly don't realise that it's wrong, and most other adults won't like to come across as superior know-alls, and correct them.
It's different with children - nobody is going to be reluctant to correct them.
I thought Peen-lope was a very weird name when I first encountered it, on some new girl's peg at school. But I was only 6, and I soon heard it pronounced as Penelope.
My brother was a voracious reader very early on, and often came across words whose meanings he could deduce from the context, but had never heard spoken.
So he'd come out with things like, 'I know it was you, so you needn't denny it!'
And 'Gribble-ayter' (as in The Rock Of)
(We still call it Gribble-ayter. ?)
I know of someone who thought 'misled' was pronounced 'mizzled' ' until long after she was grown up.