Actually zx clones in exUSSR became widely available only since 1988, when Z80 CPU was imported by tourists and workers on business trips mainly from Poland and GDR. ZX was simple (~50 ics), colorful and playful computer. In Poland commodore-64 and atari 8bit was considered too expensive and too complicated for the home usage compared to ZX at the time. mos6502 with supporting chipset was not easily available in exUSSR, also mc6845 based video is kinda expensive and complicated, it was considered as professional class chip. So, no wonder that nobody cloned expensive and not game related computer (also consider availability of schematics and components for ibm xt clones with similar to acorn bbc b prise tag and much more advanced software).