The debt with the lowest levels of interest tends to be traditional bank debt. If the company goes under, they are first in line to recover any losses. The more debt involved in a deal, the riskier it gets.

If you fund a $100m deal with $40m in debt, and $60m in equity, that's fine. That's usually low risk if it's a healthy company.

Now imagine the same deal, $80m debt and $20m in equity. Traditional banks might only give you a loan for $50m. The remaining $30m you will need to get from other investors, who will be further in line to recover any losses (meaning they will charge a higher rate of interest).

Why do banks love big deals? Easy: these deals generate a lot of profit. On a $100m loan, they'll be making $4-6m a year.

Usually the risk level is acceptable for them, since they're first in line when the company gets liquidated.

For example: a real estate business needs to use a lot more debt than a software company.