Besides size and volatily (dissolution, mergers of ETF generating unfavourable tax events), most ETF by European providers are swap-based. This means that they are cheaper/slightly better performing according to their swap risk premium, but some folks they like to stick with non-swap ETF. Finally, age --- Blackrock, Invesco etc have some of the largest and oldest ETF in the Euroepan/German market on some of the most desireable indices, and so it comes that people might not think of collecting 10 ETF on the same index but stick with one, esp. since for tax optimisation, FIFO purchase/sell order can be circumvented by collecting the same security in distinct depots.