Why say it if you don't mean it?

I am having a hard time understanding why people say things they don't mean... like why would you tell me you are okay, if clearly you're not? or why would you tell me you love me, but then treat me like you don't? Or tell me you miss me, but then never follow that up with actions? Or tell me you did something, but it's still not done? I mean... I can tell the difference.

I just don't understand.

Wouldn't life just be easier, for everyone, if we all just told the truth.

I mean... I know I'd feel less distress if people just told me the truth.