While we´re discussing theoretical maths now: It is actually a geometric thing rather than an algebraic one. The area of a square say (5*5=25) is bigger than the area of a rectangle (4*6=24) even though the combined length of the sides is equally long. If you multiply 2 numbers you always create a rectangle (or cube with 3 numbers etc). By increasing the smaller number you make the rectangle more square (bigger area), by increasing the bigger number you make the rectangle more long (smaller area).
Just for people that find graphics easier than numbers