[wongarsu]

Lots of mature companies use leverage: if you have a million to spend, you can just ask the bank to give you another two million so you can do three times as much. [1]

If you do have three million sitting around, you still have to consider if you can invest it somewhere else for more money. Why do a low-return project if you get more from investing into bonds?

And of course VCs don't get their money out of thing air, they also have to compete with all other forms of investments for money. So if short term bonds become more attractive while capital is harder to get for potential investors that puts pressure on VCs, who will pass it on.

Of course the actual dynamics are complicated and could fill books. But in the end if you are loaning money you have to do better than the cost of capital, and if you have money your own profit margin still has to outcompete other potential investments.

1: https://en.wikipedia.org/wiki/Capital_structure#Leverage