Maybe this comes down to personal preference, but I like the idea that if the continuity of a large comic universe like DC gets too cumbersome, some major events have convoluted things, or just some primary characters have had continued poor sales or writing, that we aren't left with it as readers. Plus, putting something in secondary universes pretty much automatically makes it less important and it's much harder to latch onto those characters, with a few exceptions.
In 1985, roughly 20 years after the creation of the multiverse, DC decided to reduce it down to one universe. For the most part, the main characters and their history stayed the same. In 1994, the Zero Hour Crisis was the first event that essentially re shaped the DC continuity in a broad way, I believe. In 2004, Identity Crisis launched and wasn't a Crisis in the sense that it redefined either the continuity of the DC universe or change the fundamental structure of it going forward. In 2005, Infinite Crisis brought back the multiverse. In 2008's Final Crisis, it's just a big event, and like Infinite Crisis not a lot changes about DC's continuity or structure of its universe. In 2011, DC gave use our second actual reboot of the DC universe in about 50 years of them having a multiverse, though with the ongoing Rebirth line even that is now just a 5 year period that is being folded into existing continuity.
So between 1961 and 1994 we had more or less one continuity. Between 1994 and 2011 we had a second continuity, though in 2016 it has essentially been retconned into that same single continuity.
So unless I'm just way off, which I haven't been reading comics for all that long and I'm far, far from an expert, I feel like this idea that DC is constantly throwing out its continuity is really overstated. Especially when you consider in Marvel they have an elastic timeline and universe changing deus ex machina like Mephisto as well as long running secondary universes that get folded into the primary Earth 616 universe.
And you know what, how DC is tying in the 2011-2016 New 52 continuity and the post-Crisis on Infinite Earth's
continuity is really interesting and pretty clever. The upcoming event could go a number of ways, but playing around with continuity this way has a chance of really paying off for people who care about continuity.
So I reject this sentiment regarding DC.