Those who opt for an OS approach, such as WordPress, usually use the applications initially free of charge. Open-source software is created by volunteers and available under various commons licences. Since the projects are almost entirely voluntary and therefore unpaid, the quality of work depends on the skills of the developers. If a developer discontinues an open-source software project, you will no longer have access to the application. So, you're always dependent on the developer's motivation and have no guarantee of functionality or updates.
The alternative to the classic open-source approach is the SaaS solution. Here you usually have a fixed subscription that you pay monthly. In return, you don't have to take on the development independently but benefit from a guaranteed service. This includes constant security updates as well as ongoing development, making corporate security a good solution in case of hacker attacks. With a SaaS site, there's no risk that development will suddenly stop.