I don't know a direct synonym. If you have room for a few more words, you could add the words planted and canned
to provide a contextual background or explanation for softball. (That is, could write "... no longer ask planted, canned, or safe and easy "softball" questions.")
Planted questions and canned questions frequently are softball questions in the sense of being easily answered, but the three words all have different connotations. If a politician plants a question, questions of ethics may be raised when that's discovered. The term canned is far more frequently applied to answers rather than questions, but web searches show it still being used frequently of questions.
Note, an ngrams comparison of planted/canned/softball + question shows that planted question is used far more frequently than either of the other two phrases; planted question usage has fallen in recent years, and usage of canned question risen.