An opinion from a stranger on the internet, is of fairly low value, because you can't determine what weight to put behind that individuals opinion. You don't know if they've been thinking about this problem for months, or if they just clanged together an opinion right then and there, or if their opinion was fed to them via some youtuber they watch, or any other number of ways people come to an opinion.

Whereas with books and even people within your community, it's usually a lot easier to discern or research whether or not their opinion was derived from great thought, facts and experience. I will value the opinions in a book about engineering from the chief mechanic of an F1 team for example, there's reason to think they've given the topic a great deal of attention.