Why do some singers lip synch their own songs?

Singing used to be its own thing. As in, a person stood up in front of a microphone and sang into it.

Today, entertainment rules. Bigger, better, stronger, faster. Dancing, gymnastics, stunts and stage effects can all impeded singing and most artists won't perform without at least a backing vocal track.

But because today's music is more about entertainment, style and personality than talent, no one really needs to be all that talented. As they said on the Brady Bunch, you just have to fit the suit. You'd be astonished at how many famous people can't actually sing all that well...and a little amazed at some who can.

Say what you want about the music of the 60s and 70s, but if it was on the radio, those guys were singing it for real. (Except the Beach Boys, who've always sucked live.)

They sing it with computer generated boosting / manipulation when they record it.. They simply cannot sing anywhere near as good as their voices are manipulated to sound on the recording, so they lip sinc and fake it during ""live"" performances..

maybe they couldnt replicate their recording voice or maybe they have health issues that affects their vocal chords. could be anything

Sound engineering is very hard. So many performances are set up rather quickly and the sound engineering may not be to the specifications of that particular artist. There might not be proper back up singers available or the artist might be required to perform physically demanding dances that will affect the performance.
Basically its just easier to lip sync. If they are any kind of artist they will at least lip sync but still have a live mic.
Also today some artists can't actually sing.

They're perfectionists?

$$$

Saves their vocal cords

Dancing and movements can exhaust vocals.

All are not good performers in reality.

Because they need auto tune because they aren’t that great of singers