Why is mount is forcing me to specify -t ext4 for one partition, but not the other?
i think the partition type of sdb1 is set to 83, which indicates a Linux fs like Ext4. While sdc1 seems to be set to some other type, according to your output of lsblk.
you can modify the partition type via utilities like fdisk or cfdisk. if i remember correctly, in fdisk you can change it by using the t command and then entering 83.