I see your demand more as the question, "Why limits and not options?".
Limits mean that more people will be looking for another method of grinding through the first few levels - so there'll be a third Trial that gets added, and that one gets ground instead.
The downside is that we, as players, wouldn't be doing the same thing over and over again, but the upside is that we, as players, wouldn't be doing the same thing over and over again until we'd done the DFB and DiB.
It's not a bad idea. Limiting options is often good. Too many people have been brainwashed into thinking, "more freedom always better", when it's not. Thanks merica.