A website, from the browsers prespective is nothing more than the collection of html/css/javasript files available via URLs. So, if you have the knowledge to create a website would not require more than just a simple text editor.
However, the website owners probably do not want to spend their precious time to manually edit the code of their pages, which are in that form, without the backend, are quite static and lack of the capability to dynamically connect to other platforms as well.
Nevertheless, even a state-of-the-art bare frontend requires the appropriate development environment and tooling, which significantly speeds up the development velocity and reduces the possibilities of making mistakes. However, to achive this an always up-to-date framework, like bootstrap or react is required. To be able to manage in our source code either the framework version or other, user requirement or failure related changes the application of a properly configured revison control system is reuired.
And so far we have not mentioned any backend related technologies, which makes possible to our website to sell goods or services, manage the access level of the registered visitors, send notification emails if required, and so on.
To implement and/or operate such properly set systems requires comprehensive knowledge from the technical staff. This knowledge includes the familiarity of the more frequently applied technolgy stacks, in which the layers are cooperating each other on a smooth way and cover the real needs of our customers.
For instance, a never changing virtual business card does not require the installation of a fully fledged CMS. In that case a responsive onepage would fair enough.
On the flip side, for an e-commerece site several modules and settings required including card payment facilites, analytics, seo and the conformity to the local regulatories.
Sometimes the default modules do not provide the expected uniqueness to our customers. Thanks to the flexible structure of these framewroks, however, we have the possibility to write the required extensions, without reinvent the wheel.
During the development process we apply the industry standard toolchain which includes containerized environment, version control system, automatized build- and test execution, etc.