Miami has many Israeli expats, this building specifically had many dual Israeli-American citizens and the family and friends of the victims called for the IDF to come help, the governor, and mayor ok-ed it so they came.

Many countries have disaster recovery teams specifically tasked with assisting in international catastrophes, the Israeli one happens to be a division of the IDF, probably for budgetary reasons.

because they volunteered and the Miami emergency response was willing to accept their help. They were then authorized to participate in the operations. The article lists many other countries this unit has also volunteered to help.

I think it's standard practice for one's military to help another country for example the Mexican military came to America to help during Hurricane Katrina. The military is prepared for all kinds of situations so they are probably the best government agency to help.

It sounds like a great real life training opportunity for a rescue unit, it seems like it would be hard to develop fake training exercises to simulate the challenges of a real collapse of a big building.