Thanks for being inquisitive when reading the Bible. Wish more people do the same too. Love the question.
The best explanation is that previously, Cain and Abel were making personal offerings to God. Here in Gen 4:26 was the first time mentioned that men engaged in public worship, as @brianlalor rightly puts it. See Psalm 116:17-19 as an example of “call upon the name of the Lord” as a corporate worship.
I hear some scholars differentiate that between the descendants of Cain and descendants of Seth. As prior to that verse was the account of Cain and his descendants in verse 17-24. And thus verse 25-26 was about the generation from Seth restoring the worship back to God.
Yet another view is that the author wanted to point out that the firstborn(not first child) right/blessing was transferred to Seth, after Cain’s falling away. Because it will be through Seth’s bloodline that Jesus will be born to (Luke 3:38). So the public worship was necessary to mention in order to establish that fact.
Additional trivia as a clue to this point: Seth means “appointed”, and Enosh means “people/person”, to make up God’s “appointed people”.
Today, calling on the name of the Lord is to declare ourselves believers (1 Cor 1:2).
I will be careful not to speculate on anything else beyond what is written.
Hope that helps with your question.