The simplest answer stems from the obvious point that:
- Conservatives tend to like things the way they are, or at least the way they were — the status quo as they see it — and don't want much in the way of change
- Liberals tend to dislike the status quo, or at least portions of it, and want to improve or fix it through active programs of change
This leads liberals down the path of investigation and activism, trying both to understand what is flawed in the world-as-it-is and seeking out remedies for the things they dislike. Thus they are naturally drawn to activities like academia and education, non-profit beneficial organizations, investigative media and journalism, and similar progressive vectors of change.
Conservatives are just as happy to work within the system as given, without questioning it much, because they think it's a good system that does — or eventually will — work for them (and everyone). They tend not to go into academia, education, non-profits, or many forms of media because those careers don't pay particularly well and conservatives don't have the overriding interest in understanding social flaws or overcoming social problems that might convince them to take poor-paying occupations. Conservatives only end up in those fields when they have an aspiration for fame, authority, or legitimacy (standard rewards within the status quo that can sometimes be found through academia, media, or non-profit think-tanks), or when conservatives start to problematize successful 'liberal' changes as bad and/or excessive and decide to try turning back the social clock through reactionary efforts.
There's nothing odd or mysterious about this. Why would one spend years of their lives (say) reading and writing about philosophy, or trying to help vulnerable populations, if they believe that philosophy is settled in the status quo and everyone has the potential to be successful on their own initiative? This is a natural division in any society.
A note, per Zeus' comment below. I've used the liberal/conservative distinction as though it were synonymous with the classic Rightist/Leftist distinction, which is overly-simplistic of me. Leftist liberals can sometimes 'win the day' and become technical 'leftist conservatives' defending their own status quo, as we saw in the USSR and still see in China. And likewise we occasionally see Rightists who bear down hard on the universalism of rights, liberties and social privileges and become technical 'Rightist liberals' as they insist that society must protect rights and liberties of all diverse populations.
But my point rested on the following distinction:
- Both Leftism and liberalism focus (ideally) on achieving social equity: a drive to diversify social, political, and economic access and opportunity to underserved populations
- Both Rightism and conservatism focus (ideally) on preserving status and entitlement: not wanting anyone to lose their rights, liberties, and positions in society.
This is not a zero-sum game by any means, but is often portrayed as such by both sides, with each side accusing the other of 'taking too much'. But that said, these so-called 'Leftist conservatives' have clearly given up the drive to diversify access and opportunity and thus become purely conservative, just as so-called 'Rightist liberals' lose the urge to protect unjust or irrational entitlements and thus become purely liberal. The more things change, the more they stay the same...