If you read the Hedgecock et al. paper, they observed a reduced uptake of FITC in unc-33 and unc-44 mutants which have shorter (and therefore a reduced surface area of membrane) cilia. However, beyond this, little is expanded upon regarding uptake mechanisms as I assume they assumed FITC was passively transported through the cilial membrane.
However, ASE and ASG did not appear to fill and they too are ciliated and open to the external environment like ADF, ASH, ASI, ASJ, ASK & ADL.
ASE and ASG are involved in chemoattraction, but then so are other, FITC +ve amphid neurones.
It may well be the specific roles of ASE/ASG in chemoattraction (and hence their channels and transporters) that set them aside from the other ciliated amphid neurones.
One possibility is that FITC is specifically excluded from ASE/ASG rather than it being specifically taken up by the other amphid neurones.
But this is mainly my speculation, others may nail the reason with a simple reference…