Explain why the N is not protonated by the acid catalyst in the mechanism of the Fischer esterification?

N is a better nuclophile and a better base than O. For example, the pKa of NH4+ is 9.2 whereas the pKa of H3O+ is -1.7 – this shows that H3O+ is the stronger acid (by quite a bit) which means the conjugate base of H3O+ (H2O) is a weaker base than the conjugate base of NH4+ (which is NH3). If this is the case, explain why the N is not protonated by the acid catalyst in the mechanism of the Fischer esterification performed in this lab.