CBP's priority mission is to keep terrorists out (not laborers) and they are doing it the best way they know how, which doesn't including misallocating funds for more guards to patrol the border. Doubling or even quadrupling the guards won't significantly stop border jumpers.
Agents in foreign airports, sea ports, patrolling coasts of Mexico, interior Mexican cities, the southern border of Mexico, etc... are more effective in stopping terrorists than more boots on the border.
I'll go along with their judgment on how best to allocate their assets.