I always found this hilarious, my phone won't let me swear in a text I am sending using voice to text but it will gladly boom "fuck" over my car's Bluetooth when someone sends me a text with swear words.
Since the voice recognition isn't perfect it means there is a chance it could make false positives and write a bad word you didn't say. Then people complain to Google or sue them. Similarly google search won't auto suggest offensive words or certain libelous statements (e.g. "X is a criminal", even if they are, and even if its a common search phrase.)