Secondly, mastering high school math is genuinely difficult these days. I'm a math major, I've made it through my calc courses and differential equations, but I found Algebra 2 legitimately hard. Logarithms and Trigonometric functions are counterintuitive, and not everybody is at their peak ability to buckle down and grind through things when they're struggling at age 17.
And lastly, this is pretty obviously at least in part a knock-on affect of covid, hence the extremely recent major spike. I'm not sure it's worth generalizing from "UC San Diego Students admitted in the last couple of years are struggling with high school math (because they were in high school during lockdown)" to "We shouldn't try paying mechanics more because everyone's bad at math"