More cells, each with fewer write cycles. This means that total number of write cycles doesn't increase linearly with the increase in cells. For what you say to be true, more and more blocks would have to be set aside for wear leveling, else someone could fill up the SSD to 95% capacity and have the SSD die within a few months.Next generation SSDs will of course have higher lifespan because they are greater capacity / more flash cells. That means wear leveling has much more cells to play around with and the average predictable lifespan of the unit will increase.
Better yet, when an SSD has exceeded its write cycles; it will turn read-only. So while it would mean you lost hardware, you don't lose your data.
Assuming that the bad block algorithm detects it in time. There's no 100% guarantee that this will always work. Also, generally first a block is written, then read, if the read is bad, the data is written to another block. I'm not even sure SSDs do turn read-only at some point, or will merely shrink in capacity.