The fact that they don’t mature is a general feature of bond ETF if I’m not mistaken (except for funds with a fixed maturity date). However, for rebalancing and volatility reduction purposes, I don’t see this as a problem.
I see the benefit of a known maturity date mostly where one has a fixed known date, where a predetermined amount of money has to be in cash. This is not exactly rebalancing and volatility reduction of a fund where the planned withdrawal date is far away, like for most retirement funds. Even here, volatility reduction is mostly done for unforeseen events requiring an early (partial) withdrawal. (or if you can’t mentally hold out too much volatility in your portfolio)
Ben Felix made a video about bonds funds and if I understood it correctly, a bond with fixed maturity is not really better than a bond fund with the same average maturity. It’s merely an accounting trick if one skips the reevaluation of a bond if interest rates change, since this bond couldn’t be sold at this price if required.
Do you have any further reading material about this and how large the difference in correlation between corporate and government bonds to equity is? I know that gov bonds had negative correlation in the last ~20 years, but this was not a given in the past, especially in inflationary environment, the correlation was positive