Why do we say, "shoe shop" not "shoes shop

[H0riz0n]

Hello Mr Muhsen
singular and plural : noun + noun

first noun singular: shoe shop
In noun + noun structures , the first noun is normally singular in form even if it has a plural meaning

a shoe shop (= a shop that sells shoes)

a toothbrush (= a brush for teeth) trouser poc/cets (= pockets in trousers) a ticket office (= an office that sells tickets)

exceptions
Some nouns are plural in this structure. These include nouns which have no singular form (like
clothes), nouns which are not used in the singular with the same meaning (like customs), and some nouns which are more often used in the plural than in the singular (like savings). In some cases, e.g. antique(s),drug(s), usage is divided, and both singular and plural forms are found. In general, plurals are becoming more common in this structure. Examples :
a clothes shop
a drinks cabinet
a glasses case
a goods train (British English)
a customs officer
a sports car
arms control
a greeting(s) card
a savings account
an antique(s)
dealer/shop
the accounts department
the drug(s) problem
the sales department
the arrival(s) hall
(at an airport)

the outpatients department (of a hospital)

Source: Practical English Usage, Michael Swan Page 524