Otherwise the user would have to take the ipa, get an app like altstore on a compatible computer. Sync it. Then be stuck with the limitations of sideloading like needing to refresh the authorization every 7 days.
Either way. Most people won’t do this. We saw what happened when Fortnite was off the Play Store. It wasn’t that effective.
Apple doesn't let you install Chromium/Blink, or any other browser engine, which implements things like WebUSB and background notifications, so you're stuck with the Safari browser engine.
Coinbase might have thought about it, but anyone who looks at building a PWA for iOS for any amount of time very quickly realizes that Apple has crippled it to the point of being a bad idea.
The only path would be to require jail breaking and most consumers trust that even less.