Because Topre is quality, tactile, smooth, consistent and durable, where as regular non capacitive domes are cheap, linear, mushy, inconsistent and break easy.
Not everyone slams domes. There are dome lovers, just search the forums on keytronic. If keytronic made a tenkeyless designer variable, I might have been typing on the po' man's Topre. I'm quite giddy that I type on a realforce 87U variable instead, so it is just as fine with me that they don't.
That said the Topre is not my holy grail. I like the key feel on my G80-8200 better. A Topre with an embedded numberpad and detachable number pad, even less bezel, keys not staggered, all 45g, low noise, NKRO, detachable cable, firmware programmable and waterproof board on the other hand would come very close.