Uh… we don't have the size, density, water table, or tax base to build like LA does. Sure, FDOT seems happy to pour billions into more and wider highways, but at some point the bill comes due on maintaining them, and the sprawl we have doesn't justify the cost without subsidy by other communities. We really can't afford to just build more highways forever.
JTA seems to at least be
claiming that using the Skyway infrastructure for anything other than a public transportation system (I'm not
entirely sure how the U2C qualifies as that but I digress) triggers federal payback demands, in which case converting it into an elevated pathway won't work.
I'm confused how you say that building path/trail infrastructure will not change behavior, but building new Hart Bridge ramps means "they will come," which is a change in behavior? Not to mention that the ramps have been there for decades and if anything, they took people away from Downtown more than making them come? Maybe it was an error to tear them down before the promised development was a sure thing, but nonetheless the local, state, and federal government have all invested in removing them, so we'll have to lie in that bed.
The reason a lot of the population doesn't get around on a bike is because we poured billions of dollars into building highways instead, and designed a city where most people live pretty far from much of anything. If we have infrastructure that makes it possible to bike places, and then build housing and job centers and shopping destinations around that infrastructure, people will use it. There's nothing inherently special about Amsterdam that made biking big, just that it was what they chose to invest in. We can choose that too.