Because Apple believed in making the best desktop printer with available technology at the time and cost was a secondary consideration.
The Apple LaserWriter was the first desktop laser printer that could print complex graphics at 300 dpi.
The LaserWriter had (for the time) an astounding 12 MHz Motorola 68k CPU and the enormous amount of 1.5 MB of RAM. It cost nearly $7,000 USD in March 1995.
Wow, My GameBoy has better specs than that.
You need to put this in context with the computers that were sold alongside it.
The Macintosh 128k, the original classic Mac, was also sold in 1985. It and 128 kb RAM (1/12th of the RAM in the LaserWriter). It also had an 8MHz M68k CPU and cost $2,495.
No other computer maker at the time would have dared launch a product like the LaserWriter that was considerably more powerful and expensive than the computer that it plugged into.
The LaserWriter needed this power to handle processing PostScript, which is actually quite a complex programming language, rather than sending a simple bitmap to the printer like other devices at the time used.