Should I feel bad about my resignation?

I got a job offer elsewhere, it is a decent post with better salary. Therefore, I decided to resign from my workplace. In addition, I have other reasons to resign such as 1.) No job satisfaction, 2.) Too much workload, 3.) Too much uncertainty and no clear job description 4.) Bad team work and management 5.) Reducing my benefit, 6.) don't feel value and appreciated. I am the 7th employees who are resigning this month. I understand that all my bosses are shocked and disappointed about my resignation because they do like me as I am a very hard worker. Importantly, my job is not very techical, but quite important and difficult to find a replacement. My questions are why you just appreciated me when I am leaving. Why you treat me so bad when I am around?