It is purely a guess, but they are not exactly separate products like Fisheye and Agile. It is potentially buried on the product page where you click on the addon tab. Under the Marketplace line, it mentions. the "dev tools". Atlassian could not even spell out "Development". :>).
IDE Connectors are not deprecated. They are still maintained and evolved. There are also no plans to deprecate Connectors.
I don't know why they disappeared from the download page. I will ask around and let you know if I find an answer.
UPDATE: IDE Connectors are back on the products page: https://www.atlassian.com/software
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