I don't think it's so much acceptance as inability and incompetence. Inability for a club like Dortmund, that was actually going toe-to-toe under Klopp, and then fell off a serious cliff and are really far off again. Bayern is too big to fall that far; see how quickly they recovered from Ancelotti and Kovac. Or for a club like Leipzig (or Wolfsburg or Frankfurt now), that's doing very well for their means, but is still very far off Bayern in terms of personnel, finances, and international attraction. And incompetence for clubs like HSV and Schalke, that have huge financial potential but will both be in the 2. BL next year.
That inability is surmountable of course; Frankfurt are making their way up the finance ladder, and Dortmund is fairly high up already. Give it a bit more time, and they might have gotten themselves in a place where they won't drop down as deeply anymore when they have some bad luck, and will be able to really start challenging Bayern. But it's a big gap for now.
To be fair, I suppose there may be some acceptance as well. At clubs like Leipzig, Wolfsburg, and Frankfurt, that have been far off Bayern's pace for at least a decade (Leipzig even several divisions away), it's probably considered a good accomplishment to finish second or in the CL spots. But that won't stay that way; every club will want to top what they last achieved, and Dortmund is definitely eyeing the title every single season.