Because a chord name describes the chord's role, not just the notes. The same physical fingering on the neck can sometimes carry two — or even four — possible chord names. The right name depends on which note is acting as the root, what's in the bass, and what the harmony around it is doing.
The simplest case: inversions
Take a C major chord — the notes are C, E, and G. Now rearrange them so E sits at the bottom and play the same three notes, just with E as your lowest. You haven't changed the chord, you've just put a different note in the bass. That's an inversion, usually written C/E.
If you search Fretscape for C and for C/E, many of the voicing shapes will look almost identical, just with a different lowest string highlighted. For the full background on inversions, see What's an inversion and why would I use one?.
Diminished sevenths take this to an extreme
A diminished 7th chord is symmetric — every note is the same distance from the next. Strictly in theory, the 7th of Cdim7 is a doubly-flatted 7th — B double-flat — which is the same pitch as A on a guitar. Chord tools (Fretscape included) show it as A because that's how guitarists actually read it. So Cdim7 contains C, E♭, G♭, and A. If you start the same four notes from E♭, you get E♭, G♭, A, and C — which is E♭dim7. Start from G♭, and you get G♭dim7. Start from A, and you get Adim7.
Four different names, four different roots, exactly the same notes and exactly the same shape on the fretboard. Search Fretscape for any of those four chords and you'll find the same voicings — Fretscape just shows you one name at a time, based on which root you typed or built.
What Fretscape does
When you build or type a chord, Fretscape commits to one name — the one that matches the root you chose. The voicings underneath are the playable shapes for that label. If you build the same notes with a different root in mind, the voicings will overlap heavily, because they're the same physical fingerings under a different name.
In music, the right name usually comes from the key you're in and the harmony around the chord. The same shape that reads Cdim7 in one progression might read E♭dim7 in another. Fretscape doesn't try to guess that context — it shows you the chord you asked for, and trusts you to pick the name that fits your music.