Answer

In STAR Voting, blanks are counted as zeros to ensure that voter intent is preserved and to ensure that the voting method is not giving an unfair or unintended advantage to less well known candidates.

The five star ballot and the STAR Voting rules are set up specifically to ensure that voters' votes will count the way they were intended to count, and help the candidates voters explicitly chose to support. 

For the purpose of determining the finalists who advance to the runoff, if a blank was not counted as a zero, and if the average score was used instead of the total score for each candidate, then the system would give relatively unknown candidates with a few strong supporters an unfair advantage over well known candidates with a much stronger supporter base. This is why blanks in STAR Voting are always explicitly counted as zeros.

For the purpose of post-election data analysis, the number of candidates left blank, vs those explicitly bubbled in as a 0 does provide some additional data that could be interesting for campaigns, and could be publish after the election is certified as part of the full election ballot data.