Because it's personal experience. Because I'm not Uri Geller (nice scam, gotta admire his chutzpah; he made some money, met some chicks, and had more than his fifteen-minute share). Because I make no claims to anything beyond mentioning having had some experiences (which, by the by, I did not describe; they're private, and will remain so) that had physiological effects; I can conceive no tests nor posit useful explanation for those experiences. Wheat from chaff and all but there is an accumulation of reports of several phenomena going back beyond the Vedas (or Rigas or Upanishads - I fergit the proper terminology) but reported therein and elsewhere. Some appear to be nigh universal. Kinda like where there's smoke there's fire; but it does not do to confuse smoke with fog.
Way I see it, world is flat is a straw man or something. We've known, or had the info available to informed minds, or any simple observer with the opportunity to see it, for at least a good 2,500 years or so in writing (and who knows how long before) that the world is indeed spherical - ship's masts and Earth shadow on Moon, or just plain stadiametry. World is flat is a myth we were taught as part of the Christopher Columbus gig, and a religious "truth" decreed by some bishops or whatnot.
Being unable to explain something is not of itself grounds for dismissal of a thing, an observation, or an experience. I'll give some straw back - it wasn't until within the past century that we could sneak up on an adequate explanation for seeing the daytime sky as blue.
I remember when quantum tunneling was only implied by the maths. Over time there were enough observations of something happening and shaving with Occam left few choices for what was going on; experiments were devised based on developments in observational technique. Now that weird effect is taken for granted because we found a way to get a handle on forces formerly inaccessible. Right now we're looking for gravity waves and better hints of dark matter. Oh, and toss some entanglement into the salad of "spooky stuff".
More on point, while you might be able to work up a description of consciousness in action, could you provide me an explanation of its cause and how it works? Can you detect whatever it is and measure it? So far as I know, that has not yet been done, yet most of us accept that it is a real thing if for no other reason than that's all that we have to even allow us to talk about it or any other thing in Universe. For all I know it'll be shown to be an algorithmic matrix of spin states attendant protein-protein ion exchange in the brain as a whole (how's that for hand-waving?), or an expression of the various force fields involved by Universe thinking itself with each individual brain acting as a focus locus. Right now brain science is birthing as the new rocket science, and we haven't any Chinese firecrackers let alone a Robert Goddard. I do keep an eye on Douglas Hofstadter, tho.
"....who as a species are prone to bias, self deception, and credulity" Oh, my, yes, indeed. But I prefer taking it as one individual at a time and building up rather than the other way 'round. By the same lights, we have people who look around and see neat and interesting things and try to find what they are; to describe, measure, test, reproduce results, and continually try to disprove and refine operational truths as the living process of science.
In a way, a good scientist is like a well-disciplined mentally adept three-year old: "Wow, man, what's that?" And onward to how does it work and why does it work that way and not some other way. And for everything neatly catalogued and placed on the shelf, dusting them off from time to time, looking anew, and questioning. To me, this is the magic.
We have it that Universe in finite but has no edge. We also have it that Universe is infinite but closed. Wtf? What little I know is that it is chock-full of wonder. It makes for awe, and humility. I'll go with that, with science as companion. YMMV.