Q: Why close grip lat pull down and not wide grip?

A: Use both! Variety is always good. I will often recommend close grip pulldown specifically because it allows maximum weight lifted and also because it works biceps much more than wide grip (important when training at low volume, without many bicep-isolating exercises). But variety is great, so by all means use all the different variations of grip in your training. I would just recommend stickin with one grip for the duration of a training cycle (2-3 months typically) before switching to another grip in the next program.