And you're presuming that DirectAdmin staff can continue to add features without it at some point impacting the price.
Fantastico and Installatron cost what they do because the companies that produce them have to cover their development cost, the support cost, and the profit to which they're entitled. If DirectAdmin would include similar functionality they'd incur similar costs. Which they'd have to recoup.
Not to mention that they'd be adding functionality not core to a control panel, which many users wouldn't want, and which would add more complexity to DirectAdmin.
DirectAdmin staff may certainly decide to respond to your request. The rest of us are just giving you our opinions.
Jeff