Its political warfare in that Apple wants to own both the hardware and software and ultimately ideally has a complete monopoly over all hardware. Ultimately they want to own 60% of every developer's pre-profit income, they're strangulating the future so you have attempts to make things better like react native. Its the same type of leverage that MS applied before its anti-trust trial where they destroyed web standards with IE and their desktop monopoly.
Two reasons: 1. Because Apple intentionally cripples them on its mobile operating systems. 2. Because PWAs can't harvest as much of your personal information as native apps can (regardless of platform).
A PWA is only useful if all of your features fit within the web. Many electrons apps have web versions with less features. That is the natural result of a sandbox.