A very unpleasant situation, which is another reminder that you should always read the user agreement before using any gambling site.
In my opinion, the gambling site should have programmatically made it impossible to bet from the bonus account on the listed games and introduced the necessary limits. Otherwise it all looks very much like a not entirely honest business, with its creators covering their actions with a user agreement.
It is rare for users to read the user agreement as we most of us instantly check the box about it every time whether we are just creating a social media account.
I agree that the gambling site should just automatically make the be higher than 10$ be impossible to do as it is against their rules and agreement. Also, they should not let their users and players to use the bonus on other games which doesn't support the bonus program.
Knowing that the site intentionally do these things makes me wonder if the gambling site should be trusted as for me, I think that they tricking their users about this loopholes on their agreement. But still, us users can't do anything as these are within their rules and the agreement we've agreed on when creating an account on their gambling website.