I've had both plastic and metal frogs for over 30 years and I've never had any frogs get "chewed up" without something else causing it.
Get an NMRA Check Gauge and check all your wheelsets especially locomotives. You can also use the gauge to check the tolerances of your turnout.
The use of plastic frogs is not all about cost, they are also used for electrical reasons. The higher quality turnouts that do use plastic frogs, use a very tuff engineering plastic that is very hard to damage. You get what you pay for.
Jay
C-415 Build: https://imageshack.com/a/tShC/1
Other builds: https://imageshack.com/my/albums
The two most probable causes: 1. The flangeway at the guardrail is too wide allowing the wheel flange going through the frog to hit the point of it. Even on the prototype, the function of the guardrail is to pull the flange of the opposite wheel over so it doesn't hit the point of the frog. 2. You have some wheelsets that are too wide of gauge.
And no, I don't make a cut off the sale of NMRA check gauges.
You just answered your own question. They're made like that for 2 reasons. #1 is cost to produce. It's much cheaper to put in a plastic frog than a metal one. #2 is replacement frequency. If the turnouts lasted forever, the company makes no money on replacement sales.
Take it from a former businessman, that's how it works.
Dr. Frankendiesel aka Scott Running BearSpace Mouse for president!15 year veteran fire fighterCollector of Apple //e'sRunning Bear EnterprisesHistory Channel Club life member.beatus homo qui invenit sapientiam