Figures & the Comma

Why do some people still persist in adding a comma to numbers when they have multiple digits?

Take the example "1234567890" as a single figure.

It is wholly incorrect to denote it as 1, 234, 567, 890.

It should read 1 234 567 890- with no commas, just a space between every third group of numbers (right to left).

So now you know.