one other reason is it helps keep competitors from trying to gain traffic off your COM
domain, especially if you are gaining ground and someone has gotten "mad" at you and want to try to steal traffic.
In the old days it was easier since the main domains people were familiar with were the COM/ORG/NET ones and would ignore going to another domain unless they knew it was the site they wanted.
With the plethora of TLDs now that social engineering can be done much more easily, especially if the other site can get a higher position on search engines than your site since few look at the actual domain names they visit, trusting that the search engine is giving them what they they (the user) wants.
How many of us that have been "domain shopping" have looked up a domain, saw that the COM
was taken but the ORG/NET
was available and purchased it? I know I have with a few that I eventually let die as I realized that the COM
domain was getting more traffic and making it harder to find mine.