I recently finished my PhD and continued to work at the same department as assistant professor. Amid lack of funding, and other academic joys, the department went an extra mile to procure my contract and I was assigned to interesting longterm projects. So from the academic perspective I should consider myself very lucky (most people fight for an uncertain short postdoc position), and the conditions for work are quite good in comparison to other departments in the field.
However, just a few months into the position, I decided to leave academia altogether, exclusively for financial reasons. I always accepted some pay gap in comparison to the industry, but recently I run into a few former classmates from undergrad, visited their companies to discuss collaborations, but suddenly ended up in getting a few job offers in comparison to which my current position looks quite inferior. The difference in the salary leaves me no option but to accept one of the offers. Also, since this happened I became quite demotivated to work.
I am expected to start in a few months. What would be the best communication strategy to my department? Considering that they did quite a lot, and I am in a position which looks perfect to them.
Unfortunately stating upfront the financial reason would be awkward and probably not understood, as talking about personal finances in most academic settings is frowned upon, and there is a culture which expects people to be happy with the academic salaries.