Well.. A person with a certain, considerable amount of followers can either say: "Lets face it guys - no program on the market can compete with Illustrator, Photoshop and InDesign.." and get money for it and also, depending on the popularity and the reach, the programs themselves.
Or say, hey try Affinity, their products are as good as Adobe products and they cost not much - and dont get anything.
If I get Adobe for free by recommending it, I will use it instead of Affinity - even tough I started using Affinity because the products can do so much for little money.
Affiliate programs are not evil.
Some people just live from creating tutorials, learning materials, recommendations for people who need answers to their questions.
They do what they love in life - and its only fair that they can somehow make their living out of the YouTube videos and online courses they make.
Affiliate is no MLM, or other "scheme". Who the hell would say such a thing? Only those who dont know what it means.
I am sad to hear the general tone from what seem to be employees of Serif.