Vallejo keeps winning space and choking his opponent's pieces. Next, White will connect the rooks and then double them on the c-file with O-O, Rfc1, Rc2, and Rbc1.
This is the key! Using the fact that Black did not complete development, Black cannot protect the pawn and is forced to push it. Therefore White manages to create a weak square on c4 which is extremely tasty for a knight. Note that this works because taking on e4 will favor White thanks to tactics.
Now we have won the c4-square for one of the knights, which will put pressure on d6 in combination with the g3-bishop. You have two knights: one is going to f5 and the other to c4. That is why Nd1 is stronger!
Finally a knight is arriving to c4 (Ndc4) and the black pawn on d6 will suffer a lot. The black king is also very exposed. Decisive advantage!
and Black is almost losing. We see that ...Bxd5 will not work due to tactics.