Complex sentence: In spite of this, it was not a commercial success because it was launched too late when the ZX 81/TS1000's successors, the ZX Spectrum/TS2068, were already available and the home computer market in general was dominated by Commodore, Atari and Apple.
Split into simpler sentences: In spite of this, it was not a commercial success because it was launched too late. The ZX 81/TS1000's successors, the ZX Spectrum/TS2068, were already available, and the home computer market in general was dominated by Commodore, Atari and Apple.