Currently H4 Visa holders (Spouses or family members for H1B work visa holders) cannot get a Social Security number and cannot work in the US.
This visa allows to study or volunteer in the US, but most respectable volunteering institution (such as hospitals) requires SSN for background checks. Studying is also a problem since a H4 holder student is not eligible to grants or to work to cover the high tuition cost in the US.
H4 holders are feeling "trapped" and desperate. There are a lot of stories about failed marriages and depression caused by this. There's even a facebook group with thousands of depressed H4 holders: https://www.facebook.com/groups/H4Visa/
This status causes H1B holders to think about turning back to their home country. America loses a lot of good talent due to this.