The vast majority of people I’ve known from Mexico and other countries working here illegally did just that. While I think border security is important it is only a small part of a bigger effort.
It’s almost impossible to get a tourist visa if you’re from a third world country and not over 80 yrs old. You have to prove you own property, a stable job and that you have enough financial resources to not want to stay illegally in the US. Believe me, if it was easy to fly into America no one would be sneaking across the desert.