"Kicked to the Curb"

Consider the entire text of chapter 21 but also the section on the Taft-Roosevelt Feud" found on page 877

Question: Why did the Republican Party deny Theodore Roosevelt a chance to run under the Party's banner for presidency in 1912? After taking a term off, He left his hand pick successor, William Taft to run and win the office in 1908. Taft was serviceable in those years, but Roosevelt had been epically popular in his years as president. Roosevelt was still very popular with the voters in 1912.

The decision to stick with incumbent Taft and let Roosevelt run his own Party for the presidency (Progressive Party aka 'Bull Moose Party) proved to be disastrous all concerned. The Progressive Party was a splinter group from the Republican Party which greatly weakened them in the general election.

A united Democrat Party won the day and elected Woodrow Wilson to the presidency.

Why did the Republican Party run the risk of such a break up? Why did they not stick with Theodore Roosevelt who was polling very well with the general public?