Not cheaper in general, just cheaper compared to equal or more energy efficient solutions.
Red LEDs are cheaper but less energy efficient, whilst more energy efficient solutions like e-Ink are much more expensive and suffer from the problem that they need external lighting to read because e-Ink dots are passive, not emissive.
Mind you, it’s possible to come up with solutions with Red LEDs where their slightly higher consumption is no big deal (for example, a button that need to be pressed to activate the charge-left display, so the LEDs are OFF most of the time rather than ON all the time, so ultimatelly use almost no energy because they’re usually off) but they tend to add cost (“no button” is cheaper than having a button) and increase the likelihood of failure or manufacturing defects (adding any kind of mechanical moving part to something which otherwise has no mecanical moving parts adds another, more risky class of failure modes).
In summary, using blue LEDs tends to be the Engineering-optimal solution for these devices, though not the usability-optimal one.
Exactly, blue LEDs are cheaper. So, shove them in everything, even if another color or no light at all makes more sense.
Not cheaper in general, just cheaper compared to equal or more energy efficient solutions.
Red LEDs are cheaper but less energy efficient, whilst more energy efficient solutions like e-Ink are much more expensive and suffer from the problem that they need external lighting to read because e-Ink dots are passive, not emissive.
Mind you, it’s possible to come up with solutions with Red LEDs where their slightly higher consumption is no big deal (for example, a button that need to be pressed to activate the charge-left display, so the LEDs are OFF most of the time rather than ON all the time, so ultimatelly use almost no energy because they’re usually off) but they tend to add cost (“no button” is cheaper than having a button) and increase the likelihood of failure or manufacturing defects (adding any kind of mechanical moving part to something which otherwise has no mecanical moving parts adds another, more risky class of failure modes).
In summary, using blue LEDs tends to be the Engineering-optimal solution for these devices, though not the usability-optimal one.