I would guess money plays a part. The commercial prospects for discovering a new fundamental particle and discovering a cure for prostate cancer are quite different.
Well, it depends. Is the cure for mice, or actual humans.
The Web itself got started at CERN, not in a zoology or animal testing lab. It takes a lot of time for successful innovations to diffuse throughout a broad, worldwide subculture. Just do the math.
I would wager the nature of work. It might be because maths and CS involve more work that doesn't require fancy equipment, there is lesser involvement of financial risk as compared to fields like biology or chemistry, where equipment is so expensive.
You just said it. Scientific fields are not differentiated arbitrarily; they drift apart as their experimental needs diverge. Chemistry and particle physics used to be one field, back before the cost of particle accelerators diverged from the cost of chemistry labs.
Right -- so how do the different experimental needs of each field inform their different cultures?
Return on investment pays a role. The higher the profit margin, the more competitive and "locked down" the field is. But things like national prestige and space race type international politics comes into play. Very rarely is lots of money spent on pure science - there's almost always a catch.