Their gear still needs alot of modifications (by now)...it's too big.
But the ballast can not be made small, if it is supposed to last at least some time...
Don't forget, then with components available in the industry (mainly capacitors), their temperature should not exceed ~75degC in order to achieve 100k+ lifetime (calculation based on 10khour/105degC rating of electrolytic capacitors), while with 50..60degC inside the fixture you do not have much margin...
So you need good heatsink (and that need some area), you need a means to prevent the fixture designer to put everything too close together (to avoid too high temperature inside the fixture; the ballast size is a good "argument") and/or to use cheap plastic with poor thermal conductivity (or at least the large surface will make the thermal transfer reasonable).