In the Canterbury Tales, Chaucer makes his Prioress a very genteel, uber-ladylike person. Unconvincingly refined! And "her grettest ooth was 'By Seynt Loy'" ... who is always glossed as a remarkably respectable saint, but not explained any further. The Prioress was proud of her French and spoke through her nose diligently, though her pronunciation showed that she had learnt French in the East End of London and had never been to France; however, she did seem to cotton on to a genuinely French saint!
If it is true, and not just true for Chaucer, that St Loy has the reputation of being, shall we say, wishy-washy, that could account for reluctance on the part of parents to use his name, perhaps?