Atlassian has massive network in its ecosystem. There are Jira Consultancies, 3rd party apps and plugins and deep integration into customers processes. If one element grows the whole ecosystem profits.
Secondly, Atlassian is not a bad company just because it's stock is overpriced. It might be a bad investment!
Over the short and midterm Atlassian is in some trouble because it has problems to scale the development while shifting from legacy to cloud. They will solve it. Still i expect some bad news to come.
These bad news will beat down the stock and maybe create an opportunity to buy a great company at a great price.
PS: The Atlassian invoice of my employer tripled over 1 year. You start cheap and simple and with every plugin and product you add the invoice grows. Thus to value Atlassian you have to look into revenue per customer over its life time, which is far greater than this year's revenue of the customer.