The simplest architectural style in which you can develop your application is a monolithic one. This is why many projects are started using this style. A monolithic application is just one big block, meaning that functionally distinguishable parts of the application, such as dealing with I/O, data processing, and the user interface, are all interwoven instead of being in separate architectural components. Another notable example of this architectural style is the Linux kernel. Note that the kernel being monolithic does not stop it from being modular.
It can be easier to deploy such a monolithic application than a multi-component one as there is simply one thing that needs to be deployed. It can also be easier to test, as end-to-end testing just requires that you launch a single component. Integration is easier too since, as well as scaling your solution, you can just add more instances behind a load...