12 cup percolator with plastic handle broke Why?

If the coffee maker you're referring to is the one pictured in the device page you selected, then it's made of a material called bakelite. Bakelite is pretty durable, but is susceptible to age and eventually will break down at stress points like what occurs every time you pick up the percolator.

So age is your most likely cause, but of course it can also simply be broken by being dropped or banged against something else. If you post some pictures of what you found perhaps we can help figure out what to do next. It may be possible to use some very strong glue like epoxy to put the handle back together, but we won't know until we can see what you're up against.

Adding images to an existing question - iFixit Repair Guide