While currency hedging is cheap in a 0% rate world, hedged ETFs tend to have higher fees. Paying ~0.5% on forex on both ends is better than paying 0.25%/year more over long holding periods. There's also much less choice when it comes to hedged ETFs.

The other thing is, you want to diversify geographically to protect you against weakness in your home economy, and when that happens the strength of your home currency tends to fall off. Hedging your currency risk is exactly what you don't want in that scenario.

It's been done in parts, for example Blackrock has both DE000A0F5UF5 and IE00B53SZB19 on the NASDAQ100, but after looking at liquidity/volume and performance data, few of the special-made DE ETF actually make significant sense to buy.