Why do I have a +8 advantage with only a minor piece up?

After black played 7.e5, stockfish gave me +8. I know they blundered a piece, but why is it a +8 advantage instead of a +3?

Maybe because stockfish evaluates the position not just by the material?

here is an example that with the same material eval +3

I think you'd have to be rated around 3500 to answer that. ;)

Because Stockfish is being very conservative.

Lc0 gives you a +27 in this position. :)