t͡ɬ is a phoneme in Nahuatl [0] (Voiceless alveolar lateral affricate [1] if you care to hear it), which explains why many Nahuatl words have sequences of "tl". I don't know if there's a specific reason why these words end with that sound (it doesn't have to be a suffix).

Edit: yes, it's a suffix (for Classical Nahuatl): "Non-possessed nouns take a suffix called the absolutive. This suffix takes the form -tl after vowels (ā-tl, "water") and -tli after consonants [...]" ([2]).

0: https://en.wikipedia.org/wiki/Nahuatl#Phonology

1:https://en.wikipedia.org/wiki/Voiceless_alveolar_lateral_aff...

2: https://en.wikipedia.org/wiki/Classical_Nahuatl_grammar