Because in that line, there's no point in playing d5 when the move dxe5 gives white a winning advantage.
4.dxe5 Bxf3
5.Qxf3 dxe5
6.Bc4 Nf6
7.Qb3 and white would have had an unstoppable double attack on f7 and b7.
Phildor with 4. d5
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Hey, I'm still semi-new and learning openings.
One of the one's I'm struggling to learn is the Phildor. Everything I've read about it, nothing has the move d5 in it. For example a game I'm currently in went (I'm white) 1. e4, e5, 2. NF3, D6 3. D4, Bg4 4. d5, nf6 and so on.
I was surprised to find a real lack of information of white moving to d5...Can anyone explain why?