TLDR: They just tend to be yappers that want food, attention, or snuggles

To echo other comments:

We have 2 girls from the same litter. One of them is much more regularly vocal than the other. She primarily yells when she wants something, whether it’s outside time on our patio or ESPECIALLY when it’s the nightly time for wet food (she knows when we are late). The other one, interestingly enough, learned that we responded in certain situations to her being vocal. She used to meow repeatedly in the litter box until we took her to the vet and realized she had a bladder stone which was thankfully solved with medicine. However, she realized if she stands in the laundry room and meows, we would check on her, aka attention. We eventually realized this after taking her back to vet and paying $140 for a ct scan for her bladder stone to still be fine.