Why is jdownloader not available in most software managers?
Despite it being one of the most popular and feature rich download managers out there and it being foss, it seems that most repos don't have it ( except for flahub iirc)
Is there is any reason behind that?
Not sure really; it may be because either jdownloader has a self updating function (i dont think its this one because it could be patched out like most repos patch telemetry out of audacity) or because it has very frequent updates to keep the site scrapers and downloaders working since it's a continous arms race between them and the websites ( i'm not sure if repos have nightly builds of programs or not).