This airworthiness code is applicable to
aeroplanes with a single engine (spark- or
compression-ignition) having not more than two
seats, with a Maximum Certificated Take-off
Weight of not more than 750 kg and a stalling
speed in the landing configuration of not more
than 83 km/h (45 knots)(CAS), to be approved
for day-VFR only
Why then are there some models around say 550kg MTOW? It seems pointless since if you go to the full 750kg you can build a far more useful and versatile plane, at very little extra cost.
Maybe they are limited by the engine; it seems that there is Rotax or Rotax or Rotax... and a lighter plane will accelerate proportionately faster and will need a lot less runway.
I know the UK 450kg "microlight" limit, but there are lots just above that.