The technology of dual-labeled hydrolysis probes (also called TaqMan® real-time PCR probes) exploits the 5 ́-3 ́ exonuclease activity of Taq DNA polymerase to cleave the probe. TaqMan real-time PCR probes are labeled with a fluorescent dye (reporter) at the 5´ end and with a quencher at the 3´ end.
Why choose alternative dyes instead of "genuine" dyes? First, they are cheaper, and second, they can give the same results. Another reason is that the number of suppliers who can provide modified oligonucleotides is restricted - only a patent or a licence owner is usually allowed to produce them.