Why do Germans say "es gibt"?

Germans say "es gibt" because it is the standard idiomatic way to express existence in German, equivalent to English "there is" or "there are." Literally translated, "es" means "it" and "gibt" is the third-person singular of "geben" which means "to give," so word-for-word it would be "it gives," which makes no sense in English, but idiomatically it has completely lost that literal meaning. The reason for this structure is historical and grammatical. German does not have a direct equivalent construction like English "there is." Instead, it uses this impersonal construction to introduce something that exists or is available. For example, "Es gibt viele Restaurants in Berlin" means "There are many restaurants in Berlin." "Gibt es hier eine Apotheke?" means "Is there a pharmacy around here?" The object that follows is always in the accusative case. It is used for both singular and plural, you do not change "gibt" to a plural form. You would never say "Es sind" for this purpose. It is an extremely high-frequency phrase that you need for everyday life, shopping, directions, and descriptions.