The search engines are not friendly to real estate agents. Most of the top 10 positions are held by big corporate. Your online history is very important. In fact, when you do see a real estate agent website in the top 10 for primary search terms, 95% of the time they have owned their domain with regular content growth for at least 15 years.
To get the attention of the search engines, it is important to add content through blogging and having a page with your sold properties that get regularly indexed.
If you are changing sites every few years, the search engines have to start all over with indexing your site and you could lose positioning. Having a site you own outright maintains that history.