weird position to take, considering what the viltrumites later do there…

the information he gathered was likely done over the course of centuries if not thousands of years. he wrote the information down so he wouldn’t forget it. he wrote it into books because that was his profession on earth. i suppose there could’ve been easier and less questionable ways to go about it, but this is ultimately a comic book about a space dad and his haifu space-boy.

what your speculating upon is explored in the comic later on.

I personally loved how much more development they gave to mark and his father before their big fight in the show compared to the comic. They let the relationship grow and that made the betrayal more shocking and meaningful.