What does the collocation "shrinking market" mean? What is "happening" to the market when it is shrinking?
"shrinking” is the adjective modifying the noun ‘market’ in the noun phrase "shrinking market”. The market gets smaller in size, perhaps less profitable, contracted or reduced when it is shrinking.
Well, but what does "smaller in size" or "less profitable" mean? Less profitable for (to) whom? For/to (which is the right preposition, please?) the seller or for the buyer? Or do you mean "less profitable" in general, i.e. for example if goods aren't sold at their equilibrium price (thus less profitable in general)?
A shrinking market is always going to be less profitable for the person/organization producing the goods and probably for those who act as their retailers or middlemen.
For the purchaser it means reduced availability of goods, and possibly more expensive goods as the manufacturer tries to maintain profitability.