The fact that they don’t mature isn’t unique to bond ETFs, it’s unique to funds in general. The reason is that you own shares in a fund. You do not own the underlying assets.
The same holds true for ETFs which invest in futures, life settlements, and other investments with limited terms. The underlying assets mature, but the fund keeps right on going.
Personally I don’t see too much point to using bond ETFs. For stocks, ETFs make a lot of sense because stock prices fluctuate so you want a broad diversification to keep things balanced, and the potential upside is high in relation to the cost of using a fund. But with bonds, the yields are fixed and relatively modest, so any TER is just negating from the interest you earn. To me it makes more sense to buy bonds directly.
A possible argument for a bond ETF is if you use an accreting ETF so that you make a (tax-free) capital gain instead of getting (taxable) interest.