Unix shell accounts only provide text because they are only capable of sending and receiving text characters. There are some very good reasons for utilizing Unix instead of graphic based programs. It is easy to access. Therefore, you only have to logon to your Internet Service Provider and connect to the Unix system and you are ready to go. There is no need to download or install graphic based programs on your own hard drive because your server is providing that service for you.
Some people prefer text over graphics, especially parents with children.
Unix is faster than graphic based programs. There is nothing to buy. Your server maintains the unix programs. However, if you want graphic based programs, you can spend hundreds of dollars on programs to install on your hard drive. Unix shell accounts are cheaper than graphic based accounts.