Why might powerpoint not let me adjust the height of a table row

I would start with the final slide and work my way backward.

Create your finished table on a slide and then copy that slide and paste it before your finished table slide.

Delete a row from the table, and then copy that slide and paste it before the current one, etc.

As you go forward it looks somewhat animated (no flashy effects though) as you add one row at a time

If you right click on the row or column you want to insert before, you see the context menu which has insert and delete options. Selecting the appropriate one of those gives you the columns/rows left/right or above/below. See picture. This at least means you don't have to go to the ribbon.

I have never come across shortcut keys for table row insertion (apart from TAB which adds one row on the end of a table if you happen to be in the last cell of the table).