Generally speaking, when your market share increases, so do the amount of devices you have in service. The more devices you have in service, the higher the percentage of failed devices.
The only way that makes sense is if you're making assumptions that you aren't enumerating.
If your device failure rate is say 0.5%, then how would that number change based on the number in service?
To answer, perhaps your production facility and/or procedures are known to degrade over time so the failure rate increases. Or perhaps your devices somehow degrade one another, so the more there are in the field the higher the degradation rate. Or perhaps you're speaking of manufacturers and models,
so the more manufacturers there are then the more likely it is that incompetent or malicious manufacturers will enter the market.
Whatever your reasoning, it would be nice if you mentioned it, otherwise your statement looks like a noob confusing a quantity with a rate.