An awfull tradition that served badly all the Z80 computers European games.
Seen on MSX and of course Amstrad CPC.
ZX Spectrum was very popular, but as Amstrad CPC or MSX had a good share of the market, ports on those standards were made.
To "Gain" time and money, the Speccy Codes were re-used, missing the fact that Amstrad CPC worked differently concerning Graphic capability.
As a result, many of those games used 1 bit graphics (2 colours), and were slower than their Speccy Couterparts, or even ended as Vaporware.
Some were pretty decent although.
Most of them were Video Mode 1 games.
This alowed the use of the same graphics, as graphists were an expensive and time consumming ressource for game editors.
Maybe they lacked the will to develop better porting tools (more user friendly) or simply didn't used an Atari ST for a proper Cross Development.