Discrepancy in App Store reviews and app availability for DuckDuckGo, Firefox, and Brave app

For which device? According to what I can see in the App Store on my iPhone, DuckDuckGo has 2.2 million ratings and a score of 4.9.

If you're asking about Mac apps, neither Firefox nor Brave is available in the Mac App Store. You need to download them directly from the developers' websites.

How does the number of ratings affect your ability to use a browser other than Safari?

• You will see many more reviews on the iPhone platform simply because there are many more users writing reviews. You only see the reviews, depending on the platform of the App Store you are using.
• As IdrisSeabright said, the developers of Firefox and Brave have not submitted an app on the Mac App Store, so of course you will need see them there. It is the developers of apps that add them to the App Store, Apple does not do that. Both are available on the iPhone to download in that App Store.
• Safari shows a webpage as designed by the site. Of course some sites use ads because it cost them money to host the webpage for you to view the site. You can get third party Content Blockers and add them as an Extension to Safari, but you will also see that they don't always work and will make some websites unusable. That would be due to the Content Blocker you added and why Safari does not do that by default. That would be a poor user experience.
• If you visit a website that says you must delete protections, then that is because you have installed a third party Content Blocker, blocked PopUp Windows needed for the site, or changed a Setting such as turning off JavaScript required by the website. All those are dependent on the requirements of the website. The same will be true for any web browser you use to access the website if you are turning off or blocking content required by the website.
• You are free to use any web browser you wish. I have used Firefox, Brave, DuckDuckGo, Chrome, and Edge, but still return to Safari as that is what works best for me. I have found that it uses the smallest memory footprint, is faster, and much more compatible when used in its default configuration. Your choice may be different than mine, and that is fine too.

Firefox can be downloaded here:

Firefox download

Brave can be downloaded here. Click the button that says "Get Brave for MacOS":

https://brave.com/download/

I checked all links and they downloaded to my Mac.