Better question – Why are people not makpid on the Mogen Avrohom’s zman for Krias Shema which is M’Deoraisa, and would never be maikil like the GR’A on Erev Pesach for Sof Zman Achilas Chometz – which is only M’Derabanan?
You would think that someone who ate chometz after the MG”A zman on Erev Pesach was a shaigetz.