I agree, they normally aren't mutually exclusive but Ji Yuan literally told Jing Xiu during their relationship, "Lovers can't be friends after breaking up unless they never loved each other in the first place. Why would anyone be friends when they could be lovers instead?"
Heavily implying at least for them, offering to be her friend is the same as putting the last nail in the relationships coffin. Not a perspective I personally share but I get what they're saying