Lowering standards is why a high school diploma is nearly worthless, it wasn’t always the case. If you can graduate with a high school diploma while still being illiterate, innumerate, etc. it is a signal with no entropy.
when was it not the case? as far as I know teachers have been pushing kids through to their diploma for 50 years so they could get out of their hair and into the workforce... both illiteracy and dropout rates were higher
one complication is that standards for jobs you could live off of were at that point much lower... many more people could drop out and make a living, this is less often the case now