Hiring manager wants to know why I declined..

I recently declined a job offer and the hiring manager asked for my reasons. Here’s my situation:

While interviewing I realized the management team of the new job isn't aligned with what I'm looking for. I would have a manager at the university and a manager at the school I would be housed in at my rural community. Additionally, the new role requires summer work, whereas I initially thought I’d be off during the summer. It’s also not an established program, so I’d have to build it from the ground up in a rural setting. Despite the $10-12k salary increase, I realized my current job offers flexibility and remote work during summers, which is valuable to me.

The new role seems to have more responsibilities and summer work and possibly not a good fit. I mainly don’t feel like building up the program on my own. since I live in the rural community, I want to avoid burning bridges and hopefully leave the door open for future opportunities if I’m ever laid off or if my current job ever becomes unbearable. Both my current position and the new job are in higher ed, which is a small world.

What would be the best way to communicate this to the hiring manager without burning bridges? Should I mention that a $10-12k increase isn’t worth the additional stress of summer work and no hybrid schedule? I am planning to respond to his email but don’t want to tel him all the bad things I saw? Any BS excuses y’all can think of? Or how would you approach this without ruining possibilities of working with them in a few years. Any advice is appreciated!