It's just the construction of the sentence. The verb "tratar" has several meanings. When we want to say "try to", we must always use "de". It's always "tratar de + infinitive". I don't think there's a logical explanation, it's just the structure of the sentence. I guess it's similar to English "deal with", for example. The meaning of "deal" (as in "deal the cards") is different from the meaning of "deal with" (as in "deal with it!). There's not a reason why we say "deal with" and not "deal about". It's just the structure. ¡Un saludo!

Buena pregunta .. Español es mi lenguaje y no se como explicarlo..Solo te puedo decir que es como un complemento en la horacion. .. Se usa en muchas frases .. Pero me gustaria saber la respuesta tambien..