Likely because just "why?" can come off as flip rather than indicating actual interest. Text-only forums can make it hard to show where you're coming from with

Likely because just "why?" can come off as flip rather than indicating actual interest. Text-only forums can make it hard to show where you're coming from with such a short response. Perhaps if you include a reason why you think it might be a bad idea, or speculate what might motivate their effort it would show your interest.