But I've been amazed at how many programmers don't like to have them. Why?
Even on normal keyboards I don't use it, and they are annoying because they make the mouse position awkwardly more to the right than it should be healthy for the arm (I really envy left handed people, they don't have to deal with this).
And it is next to impossible to get a keyboard without the numpad, fortunately I found two such keyboards and I have one at work and one at home (Logitech K310 and Microsoft Sculpt).
And I haven't seen in live any person that uses numpad, I always thought it is used by accountants only (and those that don't want to use two hands to enter numbers).
I only use keyboards that have low-key travel and are silent - basically anything that resembles laptop keyboard.
EDIT: Sorry for sounding a bit harsh, but keyboard-without-numpad != mechanical keyboard, which are quite niche, I wasn't aware that a niche product has a also niche variation - lack of numpad :)
The strength of the mechanical market, the reason why it's getting bigger, is not that it's mechanical and "clicky"(that's the stereotype), but that it's customizable. All of it. Case, PCB, keyswitches, keycaps, stabilizers. If you don't like the switches stock, they can be relubricated and modded with rubber O-rings. If you want a dampened response the stabilizers and keycaps can be heavier. The hobby has developed from that over the last decade - being able to take the platform and "own" it.
Yes, you can get a low-profile scissor switch design and it'll be quiet and function for years. But it will also be unmaintainable and resist even basic cleaning.