Many apps are designed with bitmap icons (png, jpg) instead if svg, so fractional scaling requires manual changes.
Also, frameworks like GTK don't have enough development resources to quickly make changes to support anything besides integer scaling. It's difficult to change to fractions if everything assumes integers.
PS: "making stuff show up bigger on a screen" works already, it's just not perfect. Windows is as far as I know the only OS coming close to doing scaling perfectly. Except Android and similar OS that were designed with fractional scaling in mind.
Many apps are designed with bitmap icons (png, jpg) instead if svg, so fractional scaling requires manual changes.
Also, frameworks like GTK don't have enough development resources to quickly make changes to support anything besides integer scaling. It's difficult to change to fractions if everything assumes integers.
PS: "making stuff show up bigger on a screen" works already, it's just not perfect. Windows is as far as I know the only OS coming close to doing scaling perfectly. Except Android and similar OS that were designed with fractional scaling in mind.