"Banyak" (big / MANY) over-rides the usual plural of tomat-tomat as "banyak" is/are also "many", so the plural for the object(s) becomes redundant.
Punya also does a similar thing.
Re: adj / gram., Bahasa = Bahasa is S P O K:
Subject, predicate, object, keterangan (information).
This almost reverse syntax for En. EN uses logical progression more than contextual spok (that's illogical captain).
eg, Info (K), pred, subj / obj.
Going back to the first, if you're interested in being luar biasa dengan kontol besar enak / kontol besar yang enak, baby (:
eg, Mereka punya banyak buku / Aku punya banyak buku. vs: Mereka punya buku-buku (they have books, not "many") / Aku punya buku-buku (I have books, not "many")
For shorthand - "aku punya buku2" = I have books. Sama2 = ur welcome. You will see this a lot in text.
(Aku cinta gadis-gadisku, goblok, iya dong! :P - I can't "punya" here, as I have used "ku" to show "mine" already)
As for the English, "Big, red tomato(es)" is following the correct syntax, although both "big, red" and "red, big" would be acceptable and understandable.
It is the order of importance of the information that is to be presented (ie, tomatoes are usually red, therefore, this is less important to say - not all tomatoes are big, but the vast majority are red. Therefore, big, red tomatoes - it's both economy and efficiency of communication).
Bahasa, "besar merah tomat" it's not following syntax - it's backwards, due to contextual SPOK. (this is why Star Trek is in English and Indonesia's govt. weren't planning moon landings 60 years ago).
If to say, "Aku punya tomat-tomat" - it sounds strange to many (lit. I have tomatoes, en = ok) If to say, "Aku punya banyak tomat" - it's more correct. (lit. I have many / much / a lot [of] tomato[es], en = hmm) If to say, "tomat-tomat itu punyaku", that's natural. (lit. tomato[es] that have many me, en = wtf??!)
It's not possible to suffix "mereka" in the same way as "aKU" and "kaMU" So:
It becomes, natural, "tomat-tomat itu punya mereka" = they have tomatoes.
SPOK = lit. Tomatoes, that, have, they. (translit to en = backwards! "that/those tomato[es] is/[are] theirs")
If I have big, red tomatoes, then I would say, "aku punya tomat merah besar", as the suffix will not work due to
"have / punya".
Bahasa, like all languages, has some rules of its own that it breaks, same as English, innit? Nowt queer as folk, arr.
Berikan aku kue kering, sekerang juga! / Sekerang juga berikan aku kue kering!