Because they'd have to talk users through allowing direct APK installs, complete with all the scary warnings.
That's going to reduce the number of customers they get a lot more than a redirect to the Play Store.
That's going to reduce the number of customers they get a lot more than a redirect to the Play Store.
It's also rather ridiculous that these services are accessible/usable/activated only via an installed app on my phone or tablet. Just make the service available via my web browser and the issue is resolved.
In the end I just don't bother with these services - N26, Monzo and now Revolut. I'll just stick with TransferWise.