Chad has kicked off a thematically linked discussion:

A response to Jonah on why science is so much work

and, Why they’re leaving a pointer to an InsideHigherEd article

My very personal response: poor math prep, lack of professional opportunities, acute labour shortages, and It Is Not A Lot of Hard Work, but it is Difficult To Do.

Chad and Jonah respond from the perspective of experimental work, which, to be fair, is the bulk of work in science; but, the same problem exists, arguably to a greater extent, in theory. People who ought to be able and eager to do science walk out on it, and it is perceived to be “too hard”.

I’ll give my perspective in a the wrong order:

People leave science because: their K-12 math preparation is inadequate and they are unable to make up for it later, either due to cognitive changes as they mature, or because they have been psychologically prepared to accept failure. They also leave because of the perception of a lack of safe career opportunities compared to professional degrees; because of the perception of high uncertainty in career opportunities and promotions; and because of the perception of a very long learning curve with very limited flexibility and requirement for high semi-involuntary mobility.

Or, in other words:
even if you’re good there may not be a job for you;
even if there is a job for you the perception of what it is you actually do is lacking;
even then you’re in dead-end low paying jobs for ever, and you may have to move somewhere you don’t want to go.

There is a large degree of truth to all these perceptions – the pay is relatively poor and promotion is slow. The uncertainty is high and only a fraction of the people who start end up in the primary career positions the science tracks are aimed at (the PhD research scientist at a lab of university).

The competition is professional degrees: medicine, law, business and others – there the work is hard and technically challenging, but the probability of someone getting through the hoops actually getting a job directly in their field is much higher. Perception is that promotion is rapid and assured and that there is a realistic possibility of high pay and choice of location.
So smart career minded people who want a rewarding technical career with rapid promotion and high pay tend to view science as a poor bet; science is left with – people who can’t help themselves, because they’re obsessive about it; people who are rich enough to not worry about paychecks and people who are poor enough that a postdoc salary seems like a good deal.

Shadowing over all of this is the math issue – it is essential to research science in almost all fields, and it pushes people out, so that they take alternative paths – either professional careers or non-science academia.
If I knew the solution to poor math education and math phobia I’d be writing an NSF proposal, not a blog article.

As for “hard work” – science is not hard work.
It is technically difficult, but let us get real – as “work” goes, science is not hard.

Addendum: I Am Not A Lawyer, but… my cousin is, and three of my close relatives are MDs.
My perception of work in the professions, is that they do indeed work very hard, and most likely worked harder through university than I did. BUT, the work was mostly rote – it was learning stuff that was already out there – precedents and principles, binary tree decision making and information dumps on which to make decisions, experiential stuff.
How and what; not why and whence.

I could be wrong, I Am, after all, Not A Laywer and have a Phoney Doctorate.