At first, you need to understand that a domain name has related with a IP Address of your web site/server which both of them have been stored on the database and server so called "Name Server". This system should be stable otherwise your web site can not be found in case of this server is down.

The Name Server and database may be not stable due to all of them has just been installed. Some time you may not find your site in case of the name server has problem.

Is the main registrar of the world. The database system (both of software and hardware) of domain name is mostly stable.

Most of them were established in the end of 1999. Some have no experience to solve many problems which occured.

Has enough fund because they provide the high quality services which can make some profit enough to survive in this high competitive business.

Focused on a low profit business. Let them have not enough cash flow to prolong their business, in some cases, because they need to allocate some of their revenue to ICANN (The Internet Corperation for Assigned Names and Numbers) and Network Solutions, Inc. This condition push some new registrars collapse.

A lot of strong and flexible supporting services because of the long experience from being the first and main registrar of the world. Whenever you have a complicated problem such as domain name transfer or registrant's information changing, they will solve it effectively and efficiently.

Some supporting services has not yet completely developed. Because they are the new registrars. So, some complicated problems have not been solved effectively and efficiently.