> "the biggest European hacker gathering and has grown into one of the most important conferences on digital transformation."
"biggest European hacker gathering" -> still most participants are from Germany, that's where the Chaos Computer Club is located. The club itself is organized into local groups all over the country (plus some in neighbor countries).
It's a balance. Congress aims to be accessible ticket cost-wise to all.
Professional interpreters cost a lot of money, and as such it's done by volunteers. There's little to be done while maintaining the spirit of the event.
Nothing prevents people from redubbing talks either, which may honestly be a good community effort.
Another argument put forward is the existence of English dubs for every video. I have found the quality of these dubs varies a lot, since they are run by volunteers and not people experienced in live translation. In some talks there can be segments without any translation, and in one case the translator even "gave up" because the speaker was talking too fast.