Not because the truth necessarily follows the majority, or the truth “changes” to fit somehow (?!), but because, absent stronger proof, the truth is, to some measure, more likely to be on the majority side. As we say in Yeshivish, it’s a “Hanhagah”, not a “Birur”.
Otherwise, She’as Hadechak couldn’t justify following the minority opinion (see Rebbe in Gemara Nidda 6a – 6b).