Poverty is nothing if not diverse. You can't judge what others are dealing with based only on what was true for your experiences.

Instacart is a SNAP/EBT vendor, so clearly they have low income customers. Some people prefer online shopping because of the stigma of using benefits in-person. For others without reliable access to transportation, delivery might be the most reasonable option. Public transit also takes time that might be better spent with family, or at your job.