It would eat the battery up over time. With your smartphone you have to plug it in and charge it every night - not something you usually want to do with a battery light.

No matter how low power, no wireless technology is no-power, and it has to check every second or so if a signal is being broadcast, using battery power.

Systems that only control light output can be wireless because they're only on while the light is on, but wireless systems that turn the light on and off would be doing that all night while you're not riding or using the bike.