For a designer to say speakers are ugly and are not allowed is essentially the same as the designer saying light fixtures are ugly and are not allowed. If the design intent is to have a room include audio reproduction at a certain quality and purpose then the designer needs to fulfil that design requirement.
The purpose of interior design is to implement chosen design objectives in an artistic, functional, and fiscally attainable way into an architectural space.
If one of the design objectives is to have a high end audio experience then use of appropriate speakers and electronics located in appropriate positions is definitely part of the interior design. And the interior designer or architect needs to incorporate them in the same way as lighting, HVAC, plumbing, or meeting fire and safety codes.
Architects and designers often object to the audio visual components that need to be incorporated into a particular space for it to serve its intended function while accepting all kinds of other components that bring nothing to the artistic side of the design.
Think of all the ugly but required functional elements of a room that get overlooked by designers on a regular basis while AV components like speakers receive objections: electrical outlets, light switches, smoke/fire alarms, HVAC grates and thermostats, holes in the walls for doors and windows, recessed lighting holes in the ceiling.
It is not that the speakers are innately ugly. It is that the designer does not accept that the speakers are required to serve the intended function of the room and need to be incorporated in the same way as the other functional and aesthetic elements of the room.