They exist. But they don't support Android apps that are unfortunately necessary. For example, any phone without WhatsApp or banking apps support is dead on arrival in Europe.
Which is why /e/ OS and Graphene OS adoption is higher than projects such as PostmarketOS (now Nura) or Ubuntu Touch, even if they are already quite mature. I daily drove Ubuntu Touch for two years in 2019 and 2020, and it's the need of Signal which made me switch to /e/.
Sailfish OS devices have good support for running Android apps.
Once upon a time WhatsApp had a j2me client…
Though I see signal usage creeping upwards. Maybe just my circle
Couldn’t the EU pass a law to require e/os/ to support WhatsApp or vice verse?
WhatsApp and my banking apps work fine on GrapheneOS (and /e/OS).