You might be great at your job, completed a PhD or built a phone App but that doesn’t mean you can write well. Writing is a craft. It’s a skill which enables a person to create clear and concise communication, and it improves with practice. Just like playing the piano, or kicking a soccer ball, you need to know what you’re doing so you can reach advanced levels.
So technically, you can write your own resume, but if you don’t know how to craft words that tell your story in the best way (not just the longest) you will create a document no one wants to read. And if you send your self-written resume to a prospective employer, it’s probably destined for the bin.
Like you, resumes evolve and they should be tailored to each different job, because no two jobs are exactly the same. As you gain more experience your resume needs to promote your new skill-set in the best possible way.
Resumes are a reflection on you, so if you want them to champion your skills, you need to seek professional help.