And then forgot they did when they accused him…

These prediction models are getting to be really good.

I don't think OP is suggesting they might have murdered him in retribution for the hack. As the article describes, there was quite a lot of animosity between the contractor Harrison and the owner of Ashley Madison, including a harassment campaign from Harrison that started two years before he killed himself and three years before the hack.

Harrison probably had the complete data from the company ready to go for any purpose. Maybe it was released with a deadman's switch or by a friend after he got suicided.