It is very common for people to adopt this approach to writing in which a second sentence will not be started until the first is finished. At each pause, the whole creative process comes to a halt. We may even have ideas about what we wish to say later in the piece of work, but it isn't easy to get these ideas onto paper. Instead, we are left searching for an appropriate word or wondering how to complete the current sentence. Of course, there are exceptions.
Some people have the intellectual strength to defeat temporary blocks.
They go to another part of their text which is already outlined, then return later to the point where they left off. However, such approaches are usually adopted only by the most confident and experienced. We know from the example of even prolific novelists that the source of fluency can easily dry up. For less experienced writers, these alternative strategies might create even more problems than they solve. If your basic approach to writing is simple and linear, jumping to a new section of text is difficult.