they said it's because SY's family went bankrupt, he was sponsored by WL's family to continue schooling but was dropped from being WL's fiance because of it. uncle, as the representative of the family, told SY that he's not deserving of WL because he cannot give her what she needs as he is now (this was before he became an actor)
right now they're just questioning whether SY is capable of protectling WL
And also when SY family was about to go bankrupt many investors pull out their money because they saw signs of bankruptcy and this move further accelerated their bankruptcy. Back then WL grandpa was one of the investors who pull out their investment to mitigate the damage towards WL family and his company even though WL family are good friends with SY family. Hence when they found out SY was trying to get close to WY and confess to her back in high school they were scared SY approached WY with ulterior motive for what they did back hence grandpa and uncle were on defense and told him to back off. On top of the fact that they felt the high school SY and his family economic status is below WL family during that time.
Now in current adult time line (10 years after high school) they’re still do not like SY because they think their WL deserve a better husband candidate compare to SY. And despite being an actor SY also have a business degree and approached WL once again. Hence it made WL grandpa and uncle question SY again for having ulterior motive (for ex scamming WL into marrying him just for her inheritance and who knows maybe schemes on taking over or taking down WL family company since he had a business degree which in grandpa and uncle mind shows he might have some interest in “business” else why would he major that),
Oh god, i forgot to reply,, Thank you guys for giving time and answering!!
Why do they hate song yan again? Or it wasn't revealed yet? Or my dumb brain had a brain fart and i forgot it? Σ( ￣□￣||)