Why can't my blog be a pillar page?

[#1]

Have just re-skinned a website and am setting up topics and pillar pages for the first time. 

On our site, we use blog pages for product pages. I wanted to create a topic for each product type and link to each of the brands/products as sub-topics. 

I've tried setting 3 different pages as the pillar page and am running into some issues. 

1.) Top-Level Pillar Page. I tried setting /Products as a pillar page with the idea that "Concentrates," "Topicals," "Tinctures," etc could each be topics that link back to that page. I thought it was working well because everything linked properly (image 1), but ultimately found this wouldn't work because I discovered that you can't link more than one topic to each pillar page. Products top-level Pillar Page

2.) Blog Pillar Page. I thought the next best solution would be to use one level down from products as my pillar pages. "Concentrates" /Concentrates, "Edibles," /Edibles, etc would each be pillar pages. This is the top landing page of my blog (each group of product pages is set up using the blog). HubSpot won't allow me to set this page as a pillar page. It doesn't show up when I search for site pages to set as a pillar page and I can't copy/paste this url in. It seems that any other page on my website - even blog posts can be set as a pillar page, but this page cannot. Why not? Blog landing Pillar Page

3.) Option 3. Use a Blog Post as a pillar page. This isn't ideal, but HubSpot will allow me to set a blog post as a pillar page. The problem is that this post is then at the same level in the navigation structure as each sub-topic that would be linking to it. Trying to link back to the pillar page in this example seems less organic, and results in all the sub-topics I've already set having broken links to this page. They would all need to be added. (I've added links on this page out to each of the sub-topic pages, but they currently don't link back to the original blog post page)Blog Post Pillar Page

My preference would be to use my website page (blog landing page) #2 as a pillar page, but for some reason I am unable to set it as a pillar. My second choice would be to use my top-level landing page as a pillar #1, but if you can only use a single topic per pillar page this won't work. Last resort would be using the blog post #3 as a pillar, but this seems less than ideal and will create A LOT of work for me to add links to each of the hundreds of sub-topic pages to get them to link to a blog post.

Any suggestions?
What is the reason I can't link to a blog page? 

Thanks,
Slicey

[#2]

The problem with the pillar page topic/subtopic structure is exactly that, what subjects do you put at what level? Because they cap the number of subtopics and topic links you might want to drill down more. 

I'd suggest each category be a pillar (edibles, concentrates, transdermal ect) and then think of the blogs you link as answering a specific question. 

"What's the difference between Solvent and Solventless concentrates?" Could be answered with a blog or two on different extraction methods depending on how you write it.

The big thing is that your blogs should answer a specific question on your map. It's useful to look at the "question" before you start writing instead of trying to shoehorn it in somewhere.

Hope that helps if you have any more questions feel free to ask.   

[#3]

It doesn't really help because those categories (edibles, concentrates, transdermal, etc) that I want to be pillar pages can't be set as pillar pages. That's my problem. If I try to set https://www.buddyboybrands.com/concentrates or https://www.buddyboybrands.com/edibles as a pillar page, it doesn't work. I'm trying to figure out why.

You can see in this screenshot, that I'm trying to paste the url https://www.buddyboybrands.com/concentrates in as the pillar page and HubSpot won't accept that url. You can see in the drop-down that Hubspot is suggestiong a different url ( a blog post ) /concentrates/concentrates as the closest url. And other urls below that which are grayed out because those blog posts are already linked as sub-topics. Blog landing Pillar Page