With technology when it’s free you are the one being sold. Your attention gets sold to advertisers, or in the case of Facebook, your data gets sold.
But on a smaller scale things like this blog are free because I’m paying for it, it’s only a few hundred pounds a year so it’s no problem, but for cases like Seth Godin’s blog he must be paying thousands of dollars a year to host his blog for free, which in turn he can leverage to promote his courses but there’s no obligation.
The difference is blogs are generous while free software is a business and they need to pay for it somewhere so it’s worth being aware that, that is the price. And, that you can opt out of paying by simply not using the service if you don’t like it.