I’ve never quite understood why some German words have tz, since the t doesn’t seem to provide any help in pronunciation as the sound it represents is already included in z.
My recent exposure is due to street names in Berlin, i.e. Tauentzienstraße, Schieritzstraße, Gubitzstraße. In the first, the t is part of ent and the z is part of zien, so I realize that may be due to the separate syllables. But that doesn’t apply to the other examples.
Other examples: schnitzen, Platz, Katze, setzen, letzt, Schatz.