I think that from a commercial perspective, developers think that 99.9% of app buyers really don't care about CSS, or have even heard of it, so they are happy with an app that disrespects CSS.
You obviously care, but annoying you only costs them one sale
I avidly read reviews before buying apps but I don't recall ever seeing one that complained about disrespected css. What people care about is apps crashing, skipping parts of text, not working with specific flavours of android...