About the missing Trump voters or about the Trump campaign not paying attention to data? I gave a citation for the former above - as for the latter, well, the evidence is contradictory. Trump said in May that he considers big data overrated [1][2], though he reversed himself in August [3].

The tricky part about using data is that it takes time to build an effective data operation. It takes time to collect the data, it takes time to analyze it, and then you need a large ground organizational effort to actually turn that data into votes. The last day for voter registration in most swing states is Oct 11, barely a week away. Even if he's recently had a change of heart, it's likely too late to do anything effective.

[1] http://elections.ap.org/content/ap-interview-trump-says-big-...

[2] http://www.wsj.com/articles/trumps-big-data-gamble-146939531...

[3] https://www.wired.com/2016/08/trump-cambridge-analytica/