how do I keep a table from splitting in Pages

Using Pages default setting for an inserted table, Move with Text and Inline with Text, the table will split on a row boundary when the row count exceeds that which can fit on the page. All other Text Wrap and Object Placement settings will truncate the table to the current page excluding the rows that do not fit on that page.

Well, the obvious answer is: reduce the size of the table so that it fits on one page, no?

if your table contains too many rows, then there's no option for Pages but to split the table across pages. What else would you expect it to do?

If you want the table to fit on one page, then it has to be small enough (either in terms of number of rows, or the size of the text within the cells) to fit.