Illegal immigration from mexico border crossings peaked in 2000 and (although fluctuating by weather) has steadily decreased since, and was lower during all of Obama compared to Bush. The “surge” you mention at the end of Obama’s term was just continuation of seasonal fluctuation and still lower than prior years. The article is misleading about the extent of illegal crossings. Pew has a good report and also good reporting in The Economist…
Republicans don’t want immigrants to become citizens because they will most likely vote for Democrats. It’s really that simple.
Border crossings plummeted last year because of a not-entirely-unrealistic fear that trump was going to go full brownshirt with his ICE troops. So a rebound this year is not a surprise, nor the fact that it’s a rebound to way less than previous levels.