Sometimes older leaves that get tall just happen to start leaning—the snake plant’s dense leaves aren’t necessarily the most structurally sound past a certain height! That said, if the leaves are soft or are starting to really bend in half, then that points to an issue, potentially.
Assess your watering habits. If you’re watering too much and not letting the plant dry out a bit between waterings, then the leaves could start to rot; they’ll get soft and start to droop. On the flip side, if you’re watering too little, this can weaken leaves as well. Make sure that you’re watering deeply (meaning that the water reaches the roots of the plant) and letting the soil dry out a bit between these deep waterings.
Another cause could be lighting. Too little light can weaken the plant over time. However, it sounds like the plant has large leaves, which suggests that it has had sufficient light to grow.
Finally, it could have to do with nutrients in the soil. Plants need nutrients to maintain and grow their leaves, roots, and so on, so consider purchasing and using a cacti and succulent fertilizer or a diluted 10-10-10 general purpose liquid fertilizer. Follow instructions on the packaging.
Sometimes older leaves that get tall just happen to start leaning—the snake plant’s dense leaves aren’t necessarily the most structurally sound past a certain height! That said, if the leaves are soft or are starting to really bend in half, then that points to an issue, potentially.