Gravitating toward complexity is inexorable because simpler systems are prerequisites of more complex systems. We see the same thing in evolution--it's not inherently directed, except in this sense of prerequisites. Systems can go from complex to simple (e.g., viruses), but complex systems cannot leap into existence -- see https://www.tedcloak.com/uploads/4/5/3/7/45374411/gregory_-_... -- they appear over time, via accretion. Scientific knowledge largely works the same way -- there are prerequisites. e.g., Einstein's concepts were seeded by the Lorentz equations, and of course Newtonian physics.

Of course biologically evolved systems don't occur unless there's some fitness function they satisfy. Well, complex software also provides desired functionality--sometimes the desire is just a result of marketing, but often it's due to real needs.