Why doesn't Google index articles on free blogging platforms?

I post articles on such platform blogs:
telegra.ph
write.as
rentry.co
sites.google.com
dev.to

The result is null. Google simply does not want to index articles on such sites. I ordered the placement of links on them, also the result is zero. At the same time, I tried to transfer the article from this platform to a regular site by the authors and the lack of the ability to add to any person. And there the article immediately got into the index. It tus out they are littered with these sites...

Why doesn't Google index articles on free blogging platforms? WordPress ...