Deciding which way to capture in this puzzle

In lichess.org/training/105855 the final move is Nxa5, which according to the engine is much better than Qxa5 which leads to a trade of queens. Could somebody explain to me why Nx is so much stronger? My feeble mind can't work out why.

With queens on the board d-pawn is a threat and it's hard to get the white's pawns rolling. If you exchange the queens, you'll have to worry about stopping them.

Hmm ... true. But that is very much a strategic consideration rather than a tactical one. Ok, good players have to combine them anyways.

Good auestion, though, @Gluybi !

Another strength in Nxa5 instead of the Queen is the Knight has a great square to hop to at B2 attacking the Queen too