In-post ads also appear in categories/archives

Why don’t you want to disable it in rules? Its like saying I want to drive my car without using the steering.

You can just disable each ad in the rules tab for archives and tags and it will only appear in single post pages.

It’s called ‘In-Post’. That means it should be only function on singular pages. A lot of people will not find it easy to disable these ads from archive/categories/author/search pages, that why it should only function on singular pages. Or at least be function when ‘entry-content’ is called not when ‘entry-summary’.

In-Post -> Inside the Post Content.
If we reserve In-Post for just singular pages we will need In-Archive, In-Category, In-Tag, In-Search, In-Custompost-Type etc etc which will become a nightmare to maintain for the majority of webmasters. Also it would defeat the purpose of using a plugin which is intended as a One time solution for Ad configuration needs. It will become a huge burden for the majority of users to insert the adsense code each time they edit a post.
Do use the Rules section to configure the same as it is a one time process to setup ads across the site (If you go to rules and disable ads for archives, categories, tags and search the plugin turns into a single post only solution). If you need to insert ads on each page manually its better to insert them directly in HTML mode of the editor or rely on a Custom Field Plugin to set it up.

Regards..

People usually add In-Post ads only to show ads on singular pages.

Who would want to display In-Post ads for every single post in archive/categories pages?

Think of it, some one to show three AdSense units in top/middle/bottom of page, they work perfectly fine, but suddenly over 30 AdSense code are running on other archive/categories/author/search pages.