Germination question

i've done from seed a couple years now. but lately, i have been trying to start in my house in egg cartons and nothing almost EVER germinates in those. i have some 6inch steel pots by the window and those are germinating. what am i doing wrong? is spinach not going to germinate at 65 degrees? they are on seed mats, but my house drops to 63 and then back up to 71. they stay moist. and are by the window