The vast majority of ideas their imaginer has conceived are useless, impractical, unrealizable, pointless, trivial, overly complex and/or their proponents incapable of either execution or funding of the idea. So whether it is secret or not does not matter.
If you are a recognized leader in your field, you often find you less talented competitors will copy every idea you have poorly. They use espionage to find your ideas early and try to beat you to market with your own ideas. This is why Apple is very secretive. All of their ideas are rapidly copied by numerous competitors. Even a rumor that Apple might be working on something is enough to get competitive startups funded. Many Apple ideas are developed under multiple iterations over several years before anyone outside the black ops team even hears a rumor about them. It would be very counterproductive for Apple to release advance notice of the next decade or even next year's new designs.
Psychologically it is often a bad idea to present ideas to the public before they are ready, during the protected incubation stage. New ideas not fully realized are often ripped to shreds by critics. It is much better to get to the stage of having a prototype before you release your design to the general public. Maintaining secrecy at the early stage can preserve the motivation of the designers and prevent burnout, and reactionary responses to poorly thought out but virulent criticism. This can be especially troublesome if a very interesting idea developed at a publicly traded corporation leaks out and then is ridiculed by a notable writer or critic. Often the result is for the project to be cancelled in order to appease shareholders and a culture of fear of innovation takes over as everyone plays it safe to avoid criticism.