もの if used to state reason doesn’t take だ unless it’s used in the subordinate clause. （素人が創作したもので、やっぱりすぐに壊れてしまった。）
This is one of the cool methods you can use to distinguish different uses of もの on the JLPT.
I just learned in class, using the Try JLPT3 book, that もの (as reason/cause) can also be used with ですから or even だから (although it will be もん then), which doesn’t seem to fit with your reply here, nor with the info on the meaning page for this grammar. That doesn’t entirely follow your subordinate clause exception, or does it? Every example sentence in the book had the から sentence/clause first and then either trailing dots or a comma followed by a second sentence/clause.
Since から can be followed with a 。. I haven’t thought of it as a subordinate clause since it can stand by itself.
You are absolutely right, ものだから、もので、ものだから can all be used to express reason/cause. If those are used at the end of the sentence, instead of もの(もん) by itself, then clause has been omitted. That’s why there are dots in TRY N3 books.
(By the way, you can use もん with ですから and もの with だから, it is a matter of style, もん is more casual and sounds a bit childish). もの(もん) by itself appears in TRY N2 book.
Another thing I wanted to express but wasn’t clear about is when expressing reason, “だ” by itself is not attached to もの. In other words “Aものだ。” is not used to express reason.
This is an easy way to distinguish it form other uses of もの (it has plenty of them) that use “Aものだ” pattern.
たものだ (used when reminescensing about something that happened (regulary) in the past, “used to”)
ものだ used to express strong feelings/opinion/advices(or commands)the .
There is also
たいものだ (coming soon) used to emphasize desire.
というものだ used to express generally accepted opinion
By the way, notice when making もの (without だ after) polite です appears before it. So:
While when you make ものだから more polite it appears after もの
I hope it clears everything!
Sorry for the confusion
So basically look carefully when だ/です comes after もの because depending on what is happening around it, it might not mean the same thing. While I guess if もの comes after だ/です it seems like it will always be reason/excuse/etc?