There are many software that have the very same goal/usage. How is it immoral to build something similar of your own?

Are you saying microsoft should have never been allowed to release Microsoft Word because Wordstar (and possibly other similar software) already existed?

Are wheel manufacturers all immoral for making wheels while we should still use the original wheel made of stone or wood[1] from the original author?

[1] I honestly don't know which came first but I would say carved stone