You are probably several generations removed from where your ancestors are originally from in Europe. But it is most likely that when they first arrived they spoke the languages of that land/lands and the holidays.
Many of the Puerto Ricans here are new..just one or two generations from being an actual Puerto Rican...so this "immigrant pride", that really ALL immigrants have, all over the world, is still there.
Keep in mind also that there are many people here from Puerto Rico who don't actually intend to keep living here but are working here because of special programs...
For instance, in my hometown more bilingual teachers were needed. The younger generation of Latinos were still in college and were not available to teach the students who needed bilingual teachers.
So people in the school district went to Puerto Rico, Costa Rica, and a few other places to recruit teachers to come and work...
Most of these people plan to go back or have already returned, but flew their flags proudly...both out of love and to draw others from their home countries to them.
One last thing: for many years Puerto Ricans were viewed as unsavory. Putting out their flags shows that they still love themselves and that they are decent and is a refutation for all the negativity that was in the media and in people's hearts about them.
