"Spam is irrelevant or inappropriate messages sent on the Internet to a large number of recipients." - https://ieeexplore.ieee.org/document/7048231
When people sign up for Gophercises, the first two emails I send them are about the course asking how the course is going, if they had issues with the player, etc.
After that they get Go related emails. Eg https://ckarchive.com/b/0vuwh9hvx32q Again, not really irrelevant given the interest in learning Go, and 99% of the people I talk to love those emails.
Maybe 3-4x per year I'll have a sale on my other paid courses. During those times people who have been on my mailing list for a set period of time (I think it is at least 10 days and have received at least 2 previous emails from me without unsubscribing, but I'd need to double check) will get a notice about the sale. I try to avoid being super annoying with those, so they will often contain useful lessons about coding with Go even if you aren't interested in the sale.
I make my living selling Go courses. I was only able to create and offer Gophercises as a free course because of this, so yes, I require an email address and I use Gophercises as a marketing tool. I try to make it a decent experience, but no matter what I do someone will always complain. I find my time is better spent helping the people who enjoy and appreciate what I am doing.
Instructional video instead of step-by-step text is a personal pet peeve. I know it's a lot easier to just record a video to show something like "how to replace the battery on a cordless vacuum" or "removing a sink basin nut" but it's often such a painful experience for consumption (watch a moment, pause, scrub back and watch again, pause, continue, pause, all with potentially gloved hands often in tight working spaces).
If we want people to create more text-based material, it needs to have similar financial incentives.