Why are Mod-10 & Mod-5 decade counters while Mod-6 & Mod-8 not?

Mod 16 Counter Circuit Diagram

Why are mod-10 & mod-5 decade counters while mod-6 & mod-8 not? Mod counters are truncated modulus counters

Counter decade asynchronous mod counters 16 diagram count ripple not clock while why nand gate show edge input inputs Counter counters modulus truncated

Why are Mod-10 & Mod-5 decade counters while Mod-6 & Mod-8 not?

MOD Counters are Truncated Modulus Counters
MOD Counters are Truncated Modulus Counters

Why are Mod-10 & Mod-5 decade counters while Mod-6 & Mod-8 not?
Why are Mod-10 & Mod-5 decade counters while Mod-6 & Mod-8 not?