Why isn't an idea like the telephone or the computer copyrighted?

...for instance if those ideas were copyrighted Alexander Graham Bell's family could claim royalties from every phone manufacturer in the world? Or can't you copyright ideas in the public domain?

Patent protection is for a limited period of time. When the patent time expires, then the product can be manufactured by anyone.
Something like a computer has changed so dramatically since it was first introduced, that the original patent would not match the current product.
Copyrights expire, and when they do, they can be used by anyone to produce derivative works.

Patents. And they have shelf lives; limited times they are in effect to promote competition and help lower prices.

As just stated - you get a patent. And, patents are made to expire over a certain period of time in order to be public friendly.

That's why drug companies get to sell their new drug for a while - then the patent runs out. Then you can get generics after that. Same idea...

Patents expire after 17 years..Im pretty sure the telephone has been around a bit longer than that

Copyrights apply to works or art & literature. Patents protect devices. A G bell did patent the telephone & became enormously wealthy. (The patent was contested as others had created similar devices). The patent has long since expired. There is no single "computer" patent because so many different ideas went into various devices that ultimately developed into what are now called "computers." However virtually every circuit & sub-system of every existing computer has a separate patent held by someone.