Views with tables have different column width with same setting
I think it is html table generic behaviour, as browser's determining widths of individual table cells are a complicated matter.  You would get the same widths if your columns had the same contents inside but since some columns are different you are getting different column widths.

Drupal views table display style outputs generic tables without any width specified.  You can influence widths by using something like the following in your theme's css

table.views-table td:nth-child(2) {
  width: 150px;
} 


Above specifies width for the 2nd TD tag of a views table. Change position of TD and width to your liking.