Because they're solid products that intergrate well with each other and with dev environments like IDEA. You can put together a free open-source solution using

Because they're solid products that intergrate well with each other and with dev environments like IDEA. You can put together a free open-source solution using many different tools, but the intergration between those tools isn't always great and opens up wider support issues (not necessarily paid support from Atlassian, but long-term maintainance). What do you propose as alternatives?