A doctoral dissertation is a great work, even if only judged by the dimensions of the project. Usually, it takes a few years to complete the materials for writing it, which is already a sufficient argument to use any type of help available. When the work is to be written in English, the requirements for the author immediately increase in exponential progress.
Lack of time is a serious problem
Limitations on the time available when writing a doctoral thesis are serious and can not be underestimated. Extending the period of preparing materials and composing the work itself means that its quality always decreases and it is more difficult to create a logical argument. And in the case of a doctoral dissertation, this is an absolutely necessary requirement to be met. Obtaining help with such activities can be a salutary factor both for the completion of work and for its quality.
English should not be underestimated
Writing a doctoral thesis in English may seem a small challenge for people fluent in this language, but even they should remember that the language has its own different forms depending on the context. Scientific work in English differs in style from colloquial speech and from press article. Each type of text has its own rules. The same applies in English, and the rules existing in English regarding scientific papers do not match the requirements for works in English. You can, of course, learn all the nuances of creating works in English, but it is better to rely on professional services.