The judge didn't block the repeal:
US district judge William Alsup rules the Daca program must remain in place while litigation over Trump’s decision unfolds.
(Emphasis mine.) Further:
The Trump administration could appeal the ruling, which could then be appealed to the US supreme court.
It makes sense because several states, organisations and individuals challenged the repeal of DACA in lawsuits. If there's a risk that Trump's administration is overturned (remember the Muslim ban?) it's more practical to postpone the DACA repeal's application until the litigation over it ends.