Interesting use of "so much"

When I use the phrase "so much," I normally mean it as a quantifier of an uncountable noun. That sounds pretty obtuse, but let me give examples:

Don't use so much sugar
The patient is in so much pain

This is similar to "Don't use so many potatoes," but you can count potatoes easily, but sugar is difficult, and pain is uncountable. Alright?

Here's the usage that confuses me:

You threw them away like so much trash. (from an episode of The Rookie)
Mama's giant cross-stitched bedspread would never be finished, and was so much ash. (from The Calculating Stars, by Mary Robinette Kowal)

Clearly, this usage is different, and it isn't meant to quantify the trash or the ash. It seems to emphasize the contrast between the subject and object (them vs trash, bedspread vs ash), and maybe to emphasize the negative aspect of the trash and ash. And yet, you could easily leave "so much" out of those sentences and not affect the meaning at all.

Am I missing a nuance?

And more importantly: Is there a name for this? Are there other phrases used in the same way? Are there rules about proper usage?

Solution 1:

You threw them away like so much trash means You threw them away as if they were trash.

like so much idiom

: like something that is
_{// The explanation sounded like so
much nonsense.}
_{// The house burned like so much
paper.}

_{Source: Merriam Webster — like so
much}

Solution 2:

This is the OED's sense 39 c. under head-word so:

c. adj. An equal sum or amount of (something).

One of the examples given is :

1885 E. Lynn Linton Autobiogr. Christopher Kirkland I. 219 Even my languages..were merely so much literary furniture.

Sense 37d. is the equivalent, for so many.

I think this sense is only used in a dismissive way, implying that whatever is compared is of little worth.

Solution 3:

Your definition is correct and applicable here: “so much” = “this amount of”. The implication is that trash or ash is all that the item is, now. It suggests ignorance, or wilful dismissal, of any other value that the item may hold (or have held).