Why does the speaker join the twenty - nine pilgrims at the inn?

The narrator begins by explaining that the pilgrims often make the pilgrimage to the shrine of Thomas Becket in April. The narrator is already in the Tabard Inn in Southwark when the prologue begins:

At this time, the host is already at the Tabard Inn in Southwark, as evidenced by these lines:

It happened in that season that one day

In Southwark, at The Tabard, as I lay

Ready to go on pilgrimage and start

for Canterbury . . .

Some nine and twenty in a company

Of sundry folk happening then to fall

In fellowship.

The narrator meets the pilgrims at the inn and strikes up a conversation. He asks to join the pilgrims on their journey.