too fat to bicycle? 300 lbs?!

[Trek420]

I am 5'10" and very long-waisted, and every bike I try seems to have me leaning painfully far forward/down. I end up with severe wrist pain very quickly. I asked at several bike shops but they don't seem to know what to suggest. I asked if they can put taller handlebars on a bike to accommodate my tall torso, and they didn't seem to know.

First off, a hale and hearty welcome to TE!

Next it sounds like we need to find you another LBS, one that can find you a proper bike fit. The answer to "can I put taller handlebars on my bike?" should never be "I don't know"

Dude, it's a yes or no question

No, but we could give you a taller stem
No, but we could give you a shorter reach stem
No, but lowering the seatpost may achieve the same goal
Yes, but let's see if a 'bent would fit you best.
Yes, we can but ... and so on.

Bet you'll find the answer here. Long live TE