Why can’t a currency be pegged to an ETF?

This might be the dumbest idea I've ever thought of, but hear me out. I'm not a particularly bright person, but I do understand that investing spare money in a diversified portfolio of broad, long‑term, low-risk ETFs that mix equities, bonds, and real estate is generally more prudent than letting cash rot inside a savings account. Despite this, most people don’t invest at all.

This feels unfair because I’m getting rich rich rich without contributing more value or working harder than others who simply aren’t investing. This got me thinking: what if the government stepped in? What if idle cash were to be made illegal? What if citizens were required by law to invest their excess cash into broad low-risk ETFs as a form of protection against poor financial habits?

Taking the idea further: if idle cash were automatically converted into ETFs, and people had to liquidate those ETFs to make purchases, why not eliminate the intermediate step in its entirety? Why not just use ETFs directly as a currency? Historically, currencies have been pegged to precious metals or other foreign currencies; why would pegging a currency to a diversified basket of equities, bonds, and real estate be any stranger?