Why can't Mechanics Source articles be put into containers like Story Source articles?
Perhaps a question for a bug report, rather than the forum. This may actually be a bug with Story Sources in whatever version you're using, as I cannot give Story or Mechanics Sources a parent in 243.
There's nothing stopping you from making new Categories in the Sources (Mechanics) Group or containing other types of Articles under a Mechanics Source, though.
(Also, Story Sources are Topics, not Articles.)
I want the broad overview article to be the container for the Foreword, History, and Various Images. ... What am I suppose to do with these articles when I can't put them in a container?
In my Paranoia realm I used a Mechanics Source as the top-level container for each product line (edition) and a custom Article category named "Product Info" for each individual product from that line. The Product Info category is in the Sources (Mechanics) Group and is a mix between what we've seen in the Source Topics/Articles from the content available on the LWD website and the import information for that content (since the category was made well before we had import/export). It includes things like a summary of the product, list of authors, cover images, the publisher product code, and ISBN number(s). I didn't put in any introductiony stuff since it was only for my use anyway.
In your case, perhaps use the Mechanics Source for product info and either make custom Categories in the Sources (Mechanics) Group or use some edited instances of General Articles for the other info.
Does that mean that articles that are on the story side can be contained in the mechanic side? And I can contain them in a Mechanic Source article?
In 243 you can't contain Topics under Articles or vice versa. If you need an Article that's similar to a Topic, use one of the generic Mechanics Categories or make a custom one.
Aside: "Various Images", as used in the sample content from LWD's website, is horrible organization in my opinion. Covers and other identifying marks should be in a Topic/Article with the other product information (likely the Story/Mechanics Source), handouts should be in a specific "(Product Name) Handouts" Topic/Article and (case depending) placed closer to where you're going to want to show them/hand them out than the information for the entire product, incidental images would hopefully have a home closer to the content they're supposed to be depicting, and advertisements for other products should be deleted. :P
You may be stuck using it for whatever products you're recreating in RW, but if you have the choice you may find better homes for your products' images.