They didn't because it was hella inefficient and they took shortcuts wherever they possibly could -- i.e., dynamic gates.
The next generation (CMOS) used about the same area -- you need at least a transistor and resistor, for an NMOS gate cell -- but the resistors get replaced by PMOS, making it much more powerful. There isn't anything wrong with making dynamic gates in CMOS still, but they probably used it as a selling point, or maybe there were, say, knock-on fab benefits that I'm not aware of. The onward march to finer feature size helps too, although I don't know that, say, nearby generation NMOS and CMOS Z80s, were very different?
Tim