Most people just don't want to deal with it. They want to focus on what they bring to the table and outsource the rest to people who specialize in, own, maintain and support that thing.
I’m not saying that people will just clone <large, established and popular software developed by large numbers of people, pre-AI>.
I’m asking why anyone would ever invest in a solo software startup, where the scale is necessarily small and achievable at low cost, and AI makes it feasible for many people or corporations to clone any idea of that scale within the time it takes to establish a foot in the market, if it looks remotely valuable.
Investment size for software plays is going to drop, and people will still invest for the same reason they do now: solving problems for people is valuable. Marginal costs dropping will bring down a lot of costs in various places, but the software itself is only part of what SaaS provides.
However, automation may likely become good enough that an SME can build the initial system to bootstrap the business. Not scale the business, but enough to prove that it's viable.