devtools::install parameter "upgrade" default value = "ask"

[HJAllen]

When installing a local package, upgrade = "ask" can become tedious. The help states:
""default" respects the value of the R_REMOTES_UPGRADE environment variable if set, and falls back to "ask" if unset."

upgrade = "ask" kind of defeats the purpose of setting the system environment variable R_REMOTES_UPGRADE as it still requires further input to function. Perhaps there is a good reason for setting default upgrade value to "ask" rather than "default"