When you hear the same (long) Gospel two days in a row, you start to pay extra attention. Yesterday for the feast of the Holy Family, there were two choices for Gospel readings; we heard the story of the Presentation of the infant Jesus in the Temple. And today, that's the Christmas season Gospel of the day. So I'm noticing Simeon and Anna a bit more.
Since this is the scene of the fourth joyful mystery of the Rosary, the Presentation is one of the Gospel stories that has been depicted in a lot of art. The artwork tends to depict Simeon as a priest of the Jewish Temple, wearing a mitre and very formal attire. But Luke's story doesn't say that Simeon was "in" the Temple (at work, as it were), or even near the Temple. (It was Anna who basically lived in the Temple precincts.) Simeon, instead, came to the Temple that day on purpose, "inspired by the Spirit."
Depicting Simeon as a priest does us a disservice by "restricting" (at least in our imagination) the "encounter" with the Lord (which is what the Presentation is called in the Eastern churches) to formal roles and occasions. Instead, Luke is telling us that Simeon lived in communion with God as he went about his daily work, and it was that ongoing communion that sensitized him to the subtle hints from the Holy Spirit that the prophecies were being fulfilled that very day.
Why did not all the people of Jerusalem perk up at that movement of the Spirit? It's not likely that the call came to Simeon and Anna alone, but from Luke's story, it seems that these two elderly people (perhaps hard of hearing) were the only ones who heard the Spirit's voice that day.