You just answered your own question. A self hosted solution requires a lot of domain and technical knowledge to set up. To you it might seem trivial, but that's an insurmountable barrier to many.
This project seems to occupy the same niche as products like Blokada. Most of the benefits of a self hosted solution, with a much lower barrier to entry.
Depending on your goal. If you just want to have an ad blocking DNS server then nextdns.io is fine. But if you also want to have some control over the privacy issue involved in using a public DNS server, you should seriously consider hosting it yourself.
Depending on your goal: I really don't like the idea all the ISPs can track what websites I visited (Verizon, ATT, and ISPs behind public WiFi). To me, my setup is a huge improvement to the status quo.
This project seems to occupy the same niche as products like Blokada. Most of the benefits of a self hosted solution, with a much lower barrier to entry.