Why not use Python?

Python is a popular language in the security field. This is most likely because of its ubiquity, short learning curve, and plethora of libraries. There are already several useful tools for security written in Python, namely Scapy for packet capturing, Scrapy for web scraping, Immunity for debugging, Beautiful Soup for parsing HTML, and Volatility for memory forensics. Many vendors and service providers also provide API examples in Python.

Python is easy to learn, and there are plenty of resources. Go is also easy to write and has a gentle learning curve. The learning curve and the ease of programming is not a major differentiating factor between Go and Python in my opinion. This biggest distinction, and where Python falls short, is performance. Python cannot compete with Go in terms of performance. Part of it is the interpreted nature of Python, but a larger factor is the global interpreter lock or GIL. The GIL prevents the interpreter from using more than one CPU worth of processing power, even with multiple threads executing. There are some ways to get around this, such as using multiprocessing, but this has its own drawbacks and limitations, as it actually forks a new process. Other options are using Jython (Python on Java) or IronPython (Python on .NET), and these have no GIL.