He thinks that if even at this late stage of the election process they still don’t know enough to make a choice, then perhaps they should do us all a favor and not vote at all.
There is a school of thought that says that the number of of truly undecided voters, those who follow politics and the election news and definitely plan to vote but are genuinely conflicted about whom to vote for, is vanishingly small and thus not worth bothering about and so there is point in expending much effort in trying to persuade them. Most of the so-called ‘undecideds’ are actually leaning towards one candidate or another but are not really engaged with the process and what they are undecided about is whether to bother to vote or not.
Nowadays, campaigns can use the public information that is gleaned from the internet to make fairly accurate assessments about the political leanings of pretty much everyone. So the so-called ‘ground game’, the effort to identify those people who likely lean towards your side and get them to the polls on or before election day, is where much of the campaigns’ efforts likely are or at least should be.