Your original premise said it was half a gig for a single variant, not all of them, you're moving goalposts. Also never in my life have I installed a "SemiBold" variant or any of those other barely different ones. Just install regular/light/heavy/bold and get on with your life.
Clicking Sans-Serif, Code Editor, from the quick picker downloads PkgTTc-SGr-losevka-34.9.0.zip
That file contains 9 font variants ranging in size from 50 to 54 megabytes.
And you need to SUM them to get the actual disk consumption. Add every 54 MB or so to get 489 megabytes (466 MiB) in total.
In contrast - NotoSansMono-VariableFont_wdth,wght.ttf - 1.7MB, gives me all the variants Iosevka needs half a gig for.
Your original premise said it was half a gig for a single variant, not all of them, you're moving goalposts. Also never in my life have I installed a "SemiBold" variant or any of those other barely different ones. Just install regular/light/heavy/bold and get on with your life.