His purpose in that paragraph is to destroy the ‘intellectualist’ conception of language, according to which the purpose of language is to encode independently existing thoughts, and to replace it with a pragmatist conception of language, according to which linguistic activity is primarily about coordinating with other people and only secondarily about imparting privately held beliefs.
In that paragraph, Wittgenstein says:
“[Animals] do not talk—-if we except the most primitive forms of language.—-Commanding, questioning, recounting, chatting are as much a part of our natural history as much a part of our natural history as walking, eating, drinking playing.”
Wittgenstein’s point being: Animals do have language, except relative to an inappropriately narrow conception of the same.
The reason, Wittgenstein holds, is that when we use language to transmit thought, what we are doing is to be understood in terms of the grunting, barking, squawking, etc. that animals use to coordinate with one another.
The reason, in other words, is that human language is to be understood in terms of these more primitive forms of communication, and not vice versa.