Today I got a couple of questions from the same person but due to how my system works for how I get questions they will be answered out of order!

So today’s question is as follows.

My second question is, why are Jacov, David, Abraham, Moses, Gideon, Elkanah, Ashur, Caleb, Esau, Rehoboam, Lamech, Jehoiada, Abijah, and probably many I've not read about have multiple wives and G'd didn't tell them it was bad? Like, with Soloman G'd is angry because his wives have foreign gods he starts worshiping. 

But he's not angry that he has more than one wife. Abraham, Jacov and David and Moses appear to be very favoured in Yhwh's eyes. He said David is righteous, yet he has loads of wives. Moses was like one of the most holy, he wrote the tablets and went upon the hill directly with G'd... The ten commandments say don't commit adultery but that seems definitely not to apply here, because shortly after G'd gives rules to Moses about multiple wives. 

Basically, why do Jewish people now not seem to practice this now, compared to Muslims and other religions? I know Genesis 2 has the "one flesh" but it doesn't seem to be applying to just 2 people as G'd says in 2 Samuel 12:7-8 that he gave wives (as a gift) and would have given twice that many. Am I just missing some information about Jewish culture/a historical context.

Indeed, and that is polygamy is allowed within the Torah but it was a Rabbi called Gershom ben Judah who suggested banning the practice which ultimately is what happened. There were quite a few reasons why this was debated and they range from:

• Ensuring a Jew’s wife is well supported and cared for.
• To stop fighting between any possible rival wives.
• To ensure no taking advantage of the wives.

There are quite a few other reasons as well such as a possible adopting of Christian practice to avoid being attacked by them but this is commonly debated if so. To answer the question however simple – it is allowed by the Torah but isn’t practised anymore for many reasons.