I’ve wondered about the fourth thing. I imagine it is the marketing/sales/business people who love ads, while the techies don’t particularly like ads, so the techies, who probably are aware of ad blockers and pi hole and the such, avoid telling their business overlords about them.
We certainly wouldn't want them to know that if they just replace their main app web server ("www" for example) with a reverse proxy such that some paths ("/ads/" for example) are proxied to the ad server while all other paths are proxied to the app server, ads would make it through to users with no way to use DNS nor IP filtering, leaving only browser extensions! Oops, did I spill the beans?
It would let advertisements reach the segment of pihole users who (don't MITM and (use a browser that doesn't offer extensions such as many default mobile browsers, or use native apps more than web browsers)). I guess that's not huge.
- Not that many people run Piholes so the return on investment isn't good.
- More complicated integrations with webmasters.
[a secret 4th thing] - I think the people who build these systems want to have this escape hatch for themselves.