Exactly - I can't tell you how many times my Motorola Droid, Galaxy Nexus and Note 3 got factory reset so I could either flash, or reflash, a custom ROM. But it was a LOT! Plus, flash memory back then wasn't nearly as robust as today's chips. All flash memory has a life span measured in read/write cycles. My 4K dashcam has a microSD card in it that is reading, writing and overwriting data 24 hours a day, 7 days a week: and it's expected to last well over a decade. I don't think you have anything to worry about.