The fundamental difference here is that bikes are ridden in a way that's fundamentally unchanged for decades. Contrary to this "settled" field of knowledge, programming is constantly invalidating itself. Even if you achieve competency in a limited field (perhaps operating system design or web development), that field will almost certainly overturn itself within 5 years for any reasonably broad definition of field. Consider what modern linux looks like compared to the original version; a lot of new techniques have emerged to address requirements.
To enter that field, this new knowledge is not "optional." It's required. The goalposts for competency aren't just shifting; they've got a nuclear power supply and tank treads and they're out of control.
In this, it is not unlike being a doctor. Their knowledge base is similarly in constant flux (although not quite so violently as ours). A doctor who does not constantly improve and update their knowledge will be a substantially worse doctor than one who does. A perfect example of this is pre-scientific doctors like homeopaths, who basically do nothing with an almost frightening level of dedication and fervor.
> Comments like yours are discouraging at least one specific subset of people from doing the one thing that can possibly help them increase their skills
I did not direct this at some 16 year old kid or a non-programmer, nor did I put it in a venue where non-tech people read. Even if I did, citing final consequence is hardly a good argument. In any case, the industry does a pretty good job of discouraging people from joining as it is. When I was in college, there was a 60% dropout rate between lower and upper division classes.