That decision makes absolute sense for most in-app browsers (that depend on WKWebView for functionality that isn't generic web browsing), but for actual browser apps, content blockers are sorely missing.
A simple, but functionally very basic app that does ad-blocking on iOS is Firefox Focus. This might cover most people's basic privacy needs, but not as a fully-functioning experience (I use this more for 'one-off' site visits, where I don't want to be tracked, see ads, or have any persistent record of my visit on the device).
But for a fully-featured browser with user-configurable content, JavaScript, CSS and ad-blocking, then the little-known iCab Mobile[0] does almost everything that a desktop browser can do in terms of privacy and content-control.
[0]https://apps.apple.com/us/app/icab-mobile-web-browser/id3081...
Prior to the built-in inspector with Firefox and later Safari/Chrome, iCab was the best web debugging tool I used. iCab lost many advantages (and disadvantages) when it transitioned from its own engine to WebKit, but it still is filled with power user features
All iOS power users should check out iCab
Yes I know.
But my reply was in response to a question specifically about ad-blocking for non-Safari browsers on iOS.
I use Firefox on iOS myself (which supports ad blocking under the name of "enhanced privacy protection") but might give it a shot.
For example, iOS Chrome definitely does show ads for me on the same pages that Firefox manages to block them on, with the same content blocker iOS settings.
Interestingly, AdGuard for Android allows full ad-blocking + cosmetic filtering in Chrome by installing a certificate that enables local MitMing of your TLS connections. I am both impressed and creeped out by this hack and how reliable it seems to work. :)