Because finding a contaminated sample of cells, extracting the DNA, successfully amplifying a clean PCR, genotyping or sequencing it, and editing your perfectly clear and uncontaminated results always takes about ten minutes. And nothing ever fails. Ever. They must pray to the PCR Gods more than I do. Oh, and not to mention they have a genetic database of every human on earth to compare their DNA to. Even if BLAST ever did grow that large, it would take hours, if not days of computational time to find the correct match.
Yeah, now whenever I watch CSI with my dad, he'll just turn to me and ask, "That's nothing like how it actually works, is it?" Nope.
And as a side note, you know you've been working on your honors thesis too long when a graph jam graph annoys you. The Y axis is horrible, and there are no error bars! I can definitely go from tissue sample to sequence data in 3 days if everything works perfectly, and I've also had it take up to two months (stupid low sodium clean up procedure!). ...I'm a nerd.