Plenty of room on the island
Have you noticed that authors often happily recommend books by other authors (even though an MBA might call them competitors)?
Not only that, but books sell best in the bookstore, right next to the other books.
It would be a stunning surprise if Tim Cook wrote a blurb for a Samsung phone. They live in a zero-sum universe, assuming that everyone is likely to only buy one or the other.
But for the rest of us, in most industries, it turns out that the real competition is inaction. Few markets have expanded to include everyone, and most of those markets (like books and music) have offerings where people buy more than one.
This means that if there's more good stuff, more people enter the market, the culture gets better, more good work is produced and enjoyed, more people enter the market, and on and on.
So encouraging and promoting the work of your fellow artists, writers, tweeters, designers, singers, painters, speakers, instigators and leaders isn't just the right thing to do, it's smart as well.