Many custom themes I've encountered recently (including Bright Theme) no longer install addons automatically. Instead, either the addon needs to handle it or the merchant needs to copy the various addon directories from the themes_repository..
In general, themes are updated when an addon is installed (or when a theme is installed). But this seems to have changed recently to be "only themes based on responsive" are updated.
Maybe they need to go back to the "base" respository for distributing addons like in V2. And have a new element in the manifest for a theme as to whether addons should install or not. Then if a merchant chooses a theme where they don't allow addons, then they can get support from the theme developer rather than addon developers having to chase down the various themes and explain to the merchant about the restrictions of the theme they've chosen.