If the Christian god intended other people to obey the Old Testament laws, why did it only tell Jews?

And it’s not as thought the Jews think of themselves as messengers spreading “God’s word” to everyone else; Christians just took the Torah (or Tanakh?), called it the “Old Testament” and claimed that the god of this book is the god of Christendom. Jews never intended their holy book to be used by anyone except Jews. If this god wanted everyone to follow the laws of this book, then why pick Jews who don’t like to share anything with non-Jews? This god picked the stingiest people on the planet! It just doesn’t make sense! If it had have picked Romans to write down its words, that would have made more sense because Romans were renowned religion spreaders. This stuff only starts to make sense when you realize it’s all mumbo jumbo, right?