To get this to work you need a tab character before the numbers.
If you're just making a numbered list, you don't need to use tabs to align on the decimal point. Just insert a fixed space called a figure space.
Make sure that your numbers are of equal width. From the Character or Control panel menu > OpenType, make sure Tabular Lining is set for numbers:
Then in front of 1., 2., etc. insert a figure space (Type > Insert White Space > Figure Space). The white space is the width of any figure. You could use multiple figure spaces if you had to with very large numbers.
Thank you both! Steve's fix worked fine so due to lack of time I'm rolling with it. I do remember having been shown a way to do this with the tab ruler, perhaps I'll stumble on that in the future. Malcom, I would mark both answers correct if possible.