I had turned down a lot of job offers till date for one/more of the following reasons:

* Poor work culture

* Lack of opportunities to learn at work

* Not a competitive pay

* Dated tech-stack

* Sensing toxic work atmosphere

* Company ridden with ivy-league grads that it boasts of during the course of interview. Sure-shot path to 2nd grade treatment should you join such place because it's not your knowledge that they see but only your certificates. [Confession: I learned this a hard way :(]