It does not cost me anything if someone else runs my software. I can still charge for it. The research and development is already paid for. The business plan goes something like this: 1) Buy software 2) Sell copies of it ... But it will not work good if other people start to make copies of it, so you make it a SaaS instead, having the software run in "the cloud" where only you can copy it.
Investors will be happy as long as the marginal cost to sell one additional copy is above zero. eg. you make a profit. How much they are willing to invest depend of how large the market is.
