Today's Rolia is a PWA (Progressive Web App), it can be installed like a regular app, and it works exactly like a regular app, but the installed size is only about 0.5% of a regular app, significantly smaller.
Such feature is not supported by Apple's iOS. People believe the reason is that Apple wants to keep the profit from it's Apple App Store, because PWA developers don't pay Apple to have their PWAs listed.
In the future Apple may change such policy. Afterall, PWA means a much greater productivity because developers don't have to double or triple the work just in order to be available in a different opeating system.