As
littlebabyjesus says Hebrew was adopted instead of Yiddish as nation building.
A new kind of Jewish society. Yiddish was the old Jewish life. Adopting Hebrew was a new start
It comes up in the book I'm reading An Army like no Other. The author, an Israeli, points out that Hebrew was a " dead " language. Not used generally for years.
This meant that the vocabulary was limited.
In practice the new Israeli state contained a whole load of people who spoke many different languages. From German to Russian.
In practice bits of Yiddish and other "slang" from various European languages got incorporated into modern Hebrew. To make up for lack of modern vocabulary in part.
Also the early IDF was made up of many recent immigrants who ended up in battalions where many languages were spoken. So a kind of mixed language was spoken. The early IDF was a melting pot. As most adult men were in it
So, according to the author, modern Hebrew isn't like the one used in religious ceremonies.
Perhaps
mojo pixy can cast light on this?
One achievement of the Zionists was to quickly build a new society.