I think the timescale point is an important one. For long timescales (and how long is long has changed over the years), government might be more likely to inves

I think the timescale point is an important one. For long timescales (and how long is long has changed over the years), government might be more likely to invest: eg. imagine the project of sending people to Moon: at the time, no private investor in the world could rival what Soviet Union or USA could dedicate to those projects — the price has gone down in a sense (or we've got richer individuals/companies), so you do see private investors in the field today, but there are always projects of the similar scale that might never happen if business returns are too far off.