I mean, I just got a 10-gig router,[1] and the stock username/password was "ubnt"/"ubnt." It's always the installer's job to set up a new username/password.
ER-XG is quite far from home WiFi router though :)
UBNT's new-ish home router series (AmpliFi) doesn't have default username/password- it needs to be set-up before using. I do think it's possible to have an open-network default configuration, but the LCD will nag you to set-up the device, and the first step of the setup is choosing a password (both for management and WiFi).
ISP's like spectrum discourage dispatching techs and opt for customer setup. And every model they give you has an 'admin/admin' or 'admin/password' setup.
[1] https://community.ubnt.com/t5/EdgeMAX-Stories/EdgeRouter-Inf...