There's no single, simple answer for it, even at the start of the second wave, Germany were tracking and tracing very well, isolating intelligently and experiencing fewer cases that our neighbours. In October, the country was still a beacon for Europe:
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What came thereafter was a period of gradual and significant growth in cases (and deaths, though still at a comparatively low level) that started overloading capacities in all areas. The magical 50 per 100,000 was not only soon cracked in several areas, but rapidly absolutely annihilated. In Berlin, areas soon ballooned to 100, then 200. Soon the whole city was well over the limit (to say nothing of areas in the far west and in Bavaria, that were even worse). Test capacities got overwhelmed, track and trace was swamped. Yet in comparison with March and April, there was and still is little tangible worry, even with things rapidly going south. Shops were as busy as ever, restaurants ditto.
Then came "lockdown light" at the start of November. The idea was to not screw the economy, so shops and schools stayed open while restaurants and bars shut again. Unfortunately, the cat was very much out of the bag at this point and the government started to lose control. The lockdown has slowed the exponential growth but hospitals/ICUs are slowly reaching capacity. Cases are still on the grow, it's no longer outbreaks here and there (see meat packing plants in the summer) but now widespread.
The only way to halt cases and deaths would be what they are planning now, which is essentially to let everyone do their Christmas shopping and then lock down hard at the end of next week. A friend at a major shopping chain (non-essential) has already shared a confidential mail from management saying to prepare for closure from 20.12 to 10.01. Things are pretty dead between Christmas and the middle of January in any case, so the idea has its merits I suppose. Schools have also gone to distance learning for first week back after Christmas. Will people, who have also become tired and jaded about the virus here as everywhere, listen? Will they stay apart over Christmas and New Year...doubtful. Panic buying? A possibility, but it wasn't really a huge issue save for March for a while.
When all's said and done, I think Germany will still be the "beacon". But still the best of the worst if you get what I mean, no European country has done superbly out of this. The popular opinion here is that we locked down so hard that we prevented the first wave, which means we are experiencing our "first wave" now instead.