It's not really like they are storing DNA sequences anyways. They use a genotyping array which just reads ~650k single nucleotide polymorphisms (SNPs).

An analogy would be 23andme has a 6.4mil page book of DNA for a single customer but they only know the position and letter of single character on every tenth page. Sure it's enough to identify someone (You can confidently use 50 SNPs to identify these days) but it's not like 23andme was ever storing a whole genome