Its simple at the start. And sorry, but with the stuff i work, its usually not enough.

OO would allow for easier code reuse, by composing objects out of pre-existing objects, something that is usually done by copy paste today. OO would enforce encapsulation and prevent global periphery fondling by serveral free running state-charts, where its really tough to find out, who in what order did flip the switch and cause a crash in 1 of 1000 runs of machinery.

List goes on... Sorry, but for my use cases the complexity is usually not completely avoidable.