You are the one that needs to read the sign again, it says if you cross other than at designated entries, you are in violation of laws and cites the laws you are violating. It does not say $5,000. is the maximum penalty either- it says you "may be subject to a $5,000. penalty." You may be subject to much more than that depending on the circumstances. It is a violation of law to illegally cross the border and each time you are caught doing so you become a repeat offender and the penalties increase. I live very near the border and I am familiar with both the signs and the reality of what happens.
I can tell you the main reason this man was deported while they sorted everything out is because he had been legally deported before and had returned, yet again illegally. Thus he was treated more harshly than others who may not have been previously deported. Just as a repeat car thief will face a harsher sentence than a first offender in most cases.
It is illegal to cross the border improperly and those who do so are criminals. It really is that simple.
It's also illegal to park on a meter without depositing enough coins to cover the time you need for an errand.
I guess most Americans are criminals then.