I think there's often a misperception, even among some scientists, that science and philosophy are competing methodologies for probing the same set of truths. They aren't at all. There might be some gray areas in highly theoretical fields of science that venture into speculations beyond the immediately available empirical evidence (I have been told by people more knowledgeable about such things than I that the science of cosmology arguably falls into this category), but generally speaking, (properly done) science and (properly done) philosophy involve the application of the same set of logical principles to very different kinds of questions.
To be fair, philosophy often presents itself as a competing methodology, so it's not surprising that a number of scientists believe it to be so.
There appear to be a number of people out there who, for whatever, reason, are anti-scientific. Some of them may be religious wingnuts who are trying to preserve the sanctity of their core beliefs from scientific disproof, some of them are political activists who are trying to find justification for their desired policies despite a total lack of factual grounding, and a lot are just dissatisfied (and jealous) "humanists" who are trying to establish some sort of intellectual superiority over the "priviledged" scientists.
And so they "compete" -- usually badly -- using more or less the only other methodology out there. Philosophy.
This is part of where philosophy gets its bad rep, I believe. You point out that "properly-done" philosophy should not and does not compete, but far too much philosophy, then, is demonstrably improperly done. And if someone looks at a group of "philosophers" and sees a large representation of the groups listed above, then it's hard to see philosophy as being a worthwhile endeavour.