You really are spending a lot of effort to defend low wages. Adorable.
Wages will not grow to meet employment demand if employers can pluck migrant workers from abroad for a lower wage. This
is reality, not justification for it.
If a company can hire migrant workers for $12 /hr instead of paying local workers the $20 /hr they'd want for the job, they are going to go the H-2B visa route. This flies in the face of your naive comment:
"If the employer cannot find workers at a given wage, the employer must raise wages until workers can be found."
They
can find workers at a given wage, they just live outside the US and companies have been doing this for a long time. The only way to prevent that is to put the US work force in a bubble, so migrant workers can't come in to displace US workers at a given lower wage.