A president doesn't just sit around twiddling his thumbs waiting for Congress to give him a bill to sign. As the perceived single leader of the country, he has the responsibility of proposing what legislation should be passed.
The impression I had from earlier discussions of this topic was that Cruz's supporters were implying that he'd do something to end the mandate once he got in office, and not qualifying it by saying he'd allow it to end *someday*.
Perhaps you should judge a candidate by what he says and does, rather than impressions of what other suggest he might do.