I think that the major issue with is the price tag.
And probably passengers expectations. Its PEY after all, but it seems that some customers are expecting to find a biz-class product.
And to be fair to SQ: I think they are not the only one struggelling with selling their PEY product. CX adjusted their seating arrangements, TK if iam not wrong entirely scrapped their PEY, LH seems also to have mixed demand.