If I want my lights to turn on and off automatically, I can just buy a mechanical timer. There's less that can fail, and what can fail is likely something I can fix. Usually by replacing the bulb.
An internet-connected smart light can fail in ways that I can't do anything about. The server that handles the request could be down. If there's voice control, the microphone might not hear me, or it can hear "Turn on the lights" as "Play 'All of the Lights'" and start playing Kanye.