The difference is that the Higgs was a necessary logical consequence of the Standard Model. Quantum loop gravity is purely speculative, much like string theory.
In the case of QM versus GR we have the very weird situation where we have two theories that are logically incompatible with each other, so we know at least one of them must be wrong. And yet neither one has ever made a prediction that has ever been falsified by experiment, so we have no guidance from nature regarding which theory is wrong or how. That's the reason that the theoretical physicists seem to be grasping at straws, and everyone is a little disappointed that the LHC hasn't done anything surprising.
While I agree with what you are saying, I'd like to add a bunch of addenda (caveats?).
The Higgs mechanism was one possible model which the standard model required, the others have now obviously been disproven thanks to the LHC. If no one had proposed this particular model, we'd still be wondering how fundamental particles gained mass and have another unexplained experimental result with the peak at 125 GeV from the data at the LHC.
Similarly, GR and QM are both extremely well tested, however GR has dark matter and energy to deal with, and we still have no real idea what that is. This could potentially point to GR being wrong, however none of us are able to come up with another theory of gravity that could incorporate this and be better than GR at this stage. If a theory of quantum gravity (or just gravity) came along that could explain dark matter quite effectively then it would be hailed as a better theory than GR.
The reason string theory and loop quantum gravity are considered completely speculative is because their predictions are so far beyond our grasp that even in the relatively far future we still have no way of confirming or denying either of them. Had they predicted things that could've been confirmed within the next century or so, I'm sure we'd all be rallying to try and confirm them. They aren't speculative so much so because we don't know which of GR or QM is wrong, but because their testability is quite precarious at this point.
I think it's not so much that the Higgs was logical; the difference with Higgs is that the Higgs was conceived as something testable from the start (I'm assuming, but it doesn't seem like a big leap, considering that particle physics has always been driven by experiments). The really big problem with untestable ideas is that they are not even science. Untestable ideas about physics are more like a peculiarly abstruse art form practiced by physicists.
>In the case of QM versus GR we have the very weird situation where we have two theories that are logically incompatible with each other, so we know at least one of them must be wrong
nope. Incompatible are only stretches of the theories into the areas where conditions contradict basic assumptions of the theories.
QM assumes fixed space-time which we know isn't true, so the QM can be true only where the difference between fixed space-time and real one is negligeable, ie. small scale/local effects. (And even at the small scale, assumption of the fixed space-time may be very limiting - who knows, may be powerful forces at local level do "bad" things to space-time too and this would be an explanation for the things like non-separability of quarks or a for a lot of others "strange" effects observed at quantum level).
GR is about real, non-fixed space-time and disregards any forces/interactions other than gravitation. Thus it is not correct when applied at local scales where other interactions overpower gravitation.
Thus stretching GR into small scale just makes a wrong physical theory the same way as stretching QM into GR space makes for a wrong theory too.
What you say is true, but it is also true that they are logically incompatible. GR assumes that matter is precisely localized and QM assumes that it is not. They can't both be right (and in fact we know that GR is wrong about this). So, for example, GR predicts that the interior of a black hole contains a singularity at a precise location, while QM (via the Heisenberg uncertainty principle) says that this is impossible.
In the case of QM versus GR we have the very weird situation where we have two theories that are logically incompatible with each other, so we know at least one of them must be wrong. And yet neither one has ever made a prediction that has ever been falsified by experiment, so we have no guidance from nature regarding which theory is wrong or how. That's the reason that the theoretical physicists seem to be grasping at straws, and everyone is a little disappointed that the LHC hasn't done anything surprising.