"Cows give milk."
Translation:गायें दूध देती हैं ।
Why isn't there a word such as होते/हेती/हेता to show the habitual aspect of this sentece?
हेता is used in generalisations when there is no other verb except for है in the sentence. In other sentences, it is mostly a matter of context.
As far as the habitual aspect goes, that is the main function of the simple present tense so this sentence would be understood as a habitual action as it stands.