Actually, the number IS the point. This is a country of LEGAL, documented immigration, not illegal invasion. Slightly fine distinction too esoteric for you to obviously grasp.
The whole of Mexico could move here and they would still be a minority. They don't want to, only about 300K a year move here without documents.
The Mexican economy is actually doing a lot better today than it was in the 1990's, so there's no incentive for them to leave.
Here's the thing... we could end the "Illegal" problem really easily without a wall, which is actually counterproductive.
1) Establish a national ID card with biometrics.
2) Require all employers to use a service to verify eligibility for employment.
3) Go after the people who try to get around the system with a vengeance.