Sans serif and display fonts in general are designed with subpixel matrices in mind. How well they succeed is another thing entirely. You could easily design a serif font that’s display friendly (see most monospace fonts) but they often invoke different feelings than a display font. That combined with the fact that Microsoft wants to push neumorphism, and font choice is part of that redesign, it makes sense to phase out calibri which was designed to fit with the flat look of metro design
Using single character variable names is always bad practice