I guess there's a few reasons for that: two polling companies, Survation and YouGov, essentially got the result correct in the end. The remainder did not, to be sure, but *this* time that was because they looked at the 2015 results, noted that a lot of likely Labour voters didn't turn out, and attempted to correct their raw data to account for this. So ComRes, for example, actually saw only a four-point lead for the Tory party in their final polls, but the turnout model "corrected" this to a 12-point lead. This time, turnout among Labour voters wasn't nearly so low...
So the polling companies had a mixed performance this time out, rather than a dismal one.