Well let's see:
The bill as a whole was given only an hour for debate, of which, realistically, only a small amount could have been given to blasphemy. On top of that, on 6 TD's turned up to debate it.
Edit: Not to mention the fact that people who are pro-Lisbon II won't want it tagged on to that referendum, because it'll give Lisbon even more negative connotations than it had last time around, and the law cannot be removed without a referendum to alter the constitution.