Its a a chaotic systems nobody really understands ;) In Germany, summer vacation lasts six weeks. The exact dates vary by state as well as from one to the next year, from the earliest (mid-June to late July) to the latest (late July to early September). This system is annoying and there were discussions to consolidate the time of vacations. But this let loose those people which income is based on the tourist season. Thus they spreaded the vacation times a little more. We were the first ones this year, starting the summer vacations at early June; the last state should start now, late August, with their summer vacations.
I totally understand the hotel owners etc. But nevertheless I - and lots of Germans as well - would prefer a more consolidated "core" vacation time instead of spreading this season over almost four months.