I should know better than to jump into this fray. But I can't help myself since this is something I've wondered about myself. Here are the reasons I've collected over the years. Often times I don't remember where I first learned of these reasons, I'm going to leave this un-cited.
How do you distinguish faith from gullibility? Perhaps faith is sometimes seen as a kind of gullibility. Few people would criticize you if you have faith "the sun will come up tomorrow" or "I have faith that I'm skillful and smart enough to support my family for the foreseeable future." It's the faith in uncommon things that raises eyebrows. To use the over-used Sagan quote: "Extraordinary claims require extraordinary evidence." It's the willingness to believe extraordinary claims on inconclusive evidence that might strike some as gullible.
How do you know what to have faith in and what not to have faith in? Why do people have faith in one religion but not another? Often it's based on what they want to believe, or what they think ought to be true. (See https://www.psychologytoday.com/us/blog/ulterior-motives/201107/you-end-believing-what-you-want-believe.) Or they will believe things based on the culture they were brought up in, while discounting equally plausible claims from cultures they weren't brought up in. Some say you know what to have faith in based on feeling. But that ignores the many who have feelings that are just as strong, but towards a different belief. Or it ignores the selection biases, conflicts of interest, and other influences that can subconsciously shape our feelings. Or it ignores the numerous times that feeling alone has proven to be unreliable. So to some, it may seem like faith is weakness if it appears that someone will selectively turn off their critical thinking skills for beliefs they have a vested interest in maintaining.
They are inflexible. There a numerous examples of this. Consider the bumper sticker "The Bible says it. I believe it. That settles it." Or this quote from Kurt Wise:
"I am a young-age creationist because that is my understanding of the Scripture. As I shared with my professors years ago when I was in college, if all the evidence in the universe turns against creationism, I would be the first to admit it, but I would still be a creationist because that is what the Word of God seems to indicate. Here I must stand."
The title of this post mentions "unexplored land/opportunity." Are you receiving criticism for exploring? Or for coming to conclusions when there is, admittedly, so much unknown? Faith may sometimes cause a person to appear close-minded: unable or unwilling to change beliefs based on new evidence or experiences. That may be a 3rd reason why faith might be seen as a weakness.
- Stereotyping. I'm sure every person of faith doesn't match all 3 of these reasons. They are more of a caricature, and that might be a fourth reason: Those people who consider you weak because of your faith may be stereotyping you.