I think one of the reasons BD etc. seem successful is they may only be going after e.g. 200 of the 20,000 names dropping on any one day. Because of their much larger client bases, Snapnames, Pool and Enom might be going after 2,000-4,000 of the 20,000 domains.
What this means in practice is that BD and the other private catchers can throw a huge amount of resources at just a handful of domains, but they are the domains that most people have their eye on (the "obviously good" domains) so there is a misplaced perception of dominance.
After all, if you're monitoring 200 great names and BD picks up 20, it looks like BD got 10% of the drop - but they only got 20 out of 20,000 i.e. 0.1% of the overall names dropping that day... it's just they know how to prioritize and, using those priorities they've established, to milk their private Registrar connections to the maximum.
And yes, recently, just like some drop catchers have faded and others have improved in performance, many of the private "big dogs" have also seen their results wax and wane. All healthy signs that we are in a vibrant, rather than stagnant, industry.