Many people use multiple accounts to get various bonus like rain. If the minimum amount increase for chat to be eligible for getting rain then those people who wagered only 100$ for those bonuses will be invalid. They have to reach 500$. So, they would not be able to spamming without reaching 500$. As a result spamming will decrease.
You sure that this will work ? Because you can set an autobet option in dice with 98% win rate, place a bet of 100-200sat and go for a walk. I'm sure that when you will be back, your amount wagered will be around $500 and you wont lose much. Yes this might help with spammers, but it not a 100% cure from them.
There are always some ways to cater the new requirements but not all gamblers know this. Many will be turned down by seeing that wagering requirement of 500$. Those who will apply this auto bet trick of 98%, will be less in number. There is no solution which is 100% perfect to stop the spammers misusing the gambling chat.