Because other tuner manufacturers have decided that their idea of "close" is good enough for you. Only Peterson's stroboscopic mechanical and Virtual Strobe™ displays can get close enough to show your instrument's pitch properly and consistently on a high definition display.
A tuner can only be accurate if its display is accurate. This may sound obvious, but can a tuner really be accurate if it only has a simple green light to indicate "in tune"? Can it tell you accurately how out-of-tune you are? Can it display with equal accuracy over the entire range? Unless it has a high-definition display, the answer is of course, NO!
LED and needle-type displays are very basic and are not capable of displaying exact pitch. For example, some tuners use LED displays but never use more than twenty lights to represent 100 cents (the span of one equally-tempered semitone, or one "half-step"). This forces them to compromise or simplify the readout. This also applies to tuners with a so-called "strobe mode".
Similarly, needle tuners have a limited number of reference points across the dial (about a dozen) which has the same effect. If you hold a switched off "LCD/needle" meter at a slant, you will see these reference points already mapped out!
Imagine a tape measure which does not show subdivisions under 1 foot. That's fine if you only want to measure the proverbial "broad side of a barn", but it's not much use in custom-fitting cabinets in your kitchen. A Peterson Strobe can accurately display any tone within its range to within 1/1000th of a semitone. If this sounds like overkill, listen for yourself. The difference will astound you!
This level of accuracy is also what allows us to offer you Sweetened Tunings™ specifically for your instrument. | 
