“When there is a YCT Hechsher , what value does it add”
It adds value to those who want better treatment of employees. They are willing to pay for it and would otherwise not eat at that place and think its important.
No one is making you eat at these places , you can go to some hemish place or any of a hundred different places to buy your food without the extra certificate. For that matter, no one is making you eat at these palces at all and no one is making the store put the certificate in the store
No one is making anyone do anything against their will.