I’ve spent some time researching this issue. Please see my link below for a demo of how a “normal” HTML form works. All HTML form drop-downs (selects) require the user to hit <ENTER> in order to select a value. While <TAB> is used to navigate from one form element to another. This is also why the Glazy select component does not allow <TAB> for selection.
So <TAB> for selection is not something that will be added to the component that Glazy uses, and after looking into the issue I agree with the maintainers of that code to keep the behaviour the same as for normal HTML form elements, in other words you must press <ENTER> to actually select the value, while <TAB> is for navigation.
Example of a simple HTML form:
Discussion of this issue in Github: