Why will Maggie never speak on The Simpsons?

Answer 1

She has officially spoken four times.

Her official first word was "Daddy" from Season Four's Lisa's First Word, but no one heard her, so as far as the family knows her first word was "Sequel" which she said at the end of The Simpsons Movie, however, in the series, Marge claims her first word was "Yah", spoken in the last episode of Season 20, Coming to Homerica.

She spoke full sentences [granted not grammatically perfect] in the second episode of Season 28,Friends and Family, in a flashback during a family argument at a therapist's office, she says "Maggie talk. Maggie talk. No one listen. Maggie never talk again."

She also said Daddily-Doodily in Season Seven's "Home Sweet Homediddly-Dum-Doodily" but no one acknowledged she said anything so evidently it was just heard as baby gibberish and not actual speech.