Because I need to have a small light portable laptop, not any 17 inches big monster. I think that no 13' laptop have numerical keyboard. I am not really keyboard-centric, but I very often need to select lots of files according to some pattern in their names and to go to Select - Select group with touchpad is really slow.
To be honest, I think that nowadays there is a lot of good laptops with high performance, good processors, SSD discs etc. which do not have numerical keyboard, so it is really pity that such useful shortcut is not available for them (I would love to have an option to set in the Settings of WinSCP to use any combination of ctrl, alt or fn + anything for this action).