1. The spouse needs to get offered a job, and have the employer file for a H1B on their behalf.
2. They can't start working until the H1B has been approved. So the employer has to be willing to hold the job until then.
3. However, filing for a h1b is not just expensive, but there is only about 30% probability that the candidate will get it since the visa is allotted on the basis of a lottery across all applicants.
4. The applications are open only once a year, in April, and there is a limit of # of applicants (IIRC 195,000 max applications) which usually gets reached in less than a month, after which you have to wait until next April. And if you are lucky enough to get it, you can start working from October onwards.
So here's the actual equation for any h1b hire. Your employer has to be willing to pay the extra legal fees, and wait for 5-15 months, for a 30% probability of you actually being legally eligible to work for them.
Now it is important to note that the Obama administration's action on this wasn't even for all spouses. It was for those spouses, whose spouses were on H1Bs _and_ had filed for a green card but due to country wise quotas or other reasons, they were on a long wait list for their green card application to be processed. For example, the current wait times for Indians for their green card applications to be processed is >10 years [1].
These spouses want to be productive employees of the economy, but a wait time of 10+ years is basically going to make it impossible to get back to the work force. The number of people who were eligible to take advantage of this H4 EAD program was estimated at about 100,000, but realistically, I would guess that only a fraction (say 20-40%) were actually going to use it. Which is a miniscule fraction of the total US work force of 152 million.
The Obama administration wasn't able to fix the deeper problems in US immigration policy, but it did this one humane thing for these spouses. The new administration hasn't shown any signs of trying to actually fix immigration, but in my opinion, as a populist xenophobic move which won't move the needle on the economy, the Trump administration wants to undo even this small step.
