Explorer opening database looking strange

 When I analyse a game I played I looked at this position. The opening explorer database is based on "grandmaster games", but the 4 moves in the database doesn't take the hanging queen, which is the obvious best move even for a beginner like me (engine also confirms taking the Queen is by far the best move). How can this be?

Opening databases are not move order aware but are based on positions.

If you look at those games after Re1 you'll see that the last move was Nd4 and not Re1

But regardless how this position is reached, whites best move must be to capture the Queen. I can't see how the move order can change that.

Again, the database is not move based. It is showing positions that have all the pieces on their respective squares after the listed piece is on the given square. There are no games in the master database where the queen was on c6 and the knight was already on d4 and the move Re1 was played.

The database is showing there are 4 games where white had a rook on e1 and knight on d4 with black's queen was in c6 with black to move. It's literally showing the position with all those elements on those respective squares.

As I said, if you look at those 4 games, not one of them had the possibility of capturing the queen since the last move by white was Nd4, not Re1. Opening databases are not move order dependent.

The database is showing there are four games with the position on the board with WHITE to move. And in all those four games white played Rook to E1.

That is not what the database is showing. It's showing that after the rook is on e1, there are 4 games in the database where all those pieces are on the same squares and in that particular case, it will then be black to move.

Once again, the database does not care about move order. It is just showing positions where all the pieces are on the corresponding squares and the Re1 games are those games where the rook is on e1 and all the other pieces are on those squares; it is not the move order

OK now I understand what you mean.

But is this the same database that for example chess Youtuber Daniel Naroditsky refers to when he says for example "most popular move is..." and "... has only been played four times". Because as you describe it, you can not tell from the database how popular a move is at a certain position. 

I'm pretty sure these are the four games that are being mentioned:

https://www.chess.com/games/search?fen=r1b1kb1r/1p1p1ppp/p1q1pn2/8/3NP3/2N5/PPP2PPP/R1BQR1K1%20b%20kq

The given options will correspond with the move order in many cases, but in many others there will be positions reached by transposition. So all the given positions may not be by that move order and there will be cases, such as this one, where it looks like an obvious move was overlooked or an illegal move was made 

That distinction can trip people up very easily and someone blindly following the DB without realizing it, may end up in trouble.

But why do they chose to show it like this?

To me it seems more logical and valuable for analysing to show

"In this position, move X was played in Y numer of games"

rather than

"In this position, you can play move X and reach a position that has been reached in Y number of games (but not necessarily from this position).

It's useful to know what happens in similar positions and will provide all games reaching that position, regardless of the move order.