Well, you need to arrive at a balance. To splice you need the splicing equipment and personnel. With a field mountable fast connector, it becomes easy and quick. Time is money.
Sure the field assembly kit has higher loss (0.3 db vs 0.1 db?) but the way they have the things setup maybe it is okay. I'm sure they'd have did a cost benefit analysis of both approaches and probably determined that using a field assembly kit is beneficial for them. When they calculated the PON power budget, the loss due to a field kit may have been included in it.
Even Spectra does that in some areas, their equipment comes with the SC connectors so they just use a pre fabricated cable instead of splicing on the field.