The reason is that your credit score is impacted by both your available credit (higher is better) and credit utilization (lower is better). When you pay of the last of a home loan and close that account, your available credit goes down and your credit utilization goes up (assuming you had any other debt). Both of those hurt you. When you pay the credit card down to $0 and leave it open, your available crediot stays the same and your utilization goes down.
That being said, there's an innocent explanation for this specifically. BYPL is pretty new as a common type of debt (became popular in the last five years). They're putting it into FICO 10. The last time they updated FICO was FICO 9 which was released in 2014, before that there was FICO 8 in 2008... a lot of banks are still using FICO 8 or even earlier models. Banks are slow to change, and FICO moves slowly because banks don't want their models upended every year. Fwiw if the government was more involved in this I doubt it would be taken into account any faster.
It can have a short term impact, sure, but long term (a few years), your score will be fine. I paid my last student loans years ago and I did see a sudden score drop and not I'm sitting right below 800 with no debt.
[1] https://dwp.dmdc.osd.mil/dwp/api/downloadZ?fileId=136507&gro...
Blaming poor people for being scammed only benefits grift culture.
But since this site is essentially a growth engine for grift its unsurprising to find parrots of this "poor people are moral and ethical inferiors"