Why did Indian national congress change its goal from swaraj to purna swaraj?

The INC changed its goal from Swaraj to Purna Swaraj because of the following reasons:

• The attitude of the British government compelled the national leaders to adopt the the goal of complete independence. Continued economic exploitation of the Indians by the British angered the leaders.
• Discontentment over Simon Commission which did not include any of the  Indian member.
• Brutal oppression a by the British of the demonstrators and death of Lala Lajpat rai angered the nationalist leaders.
• Vague offer of Dominion status did not satisfy the Indian leaders.
• Thus, the pledge of Purna Swaraj was taken at the Lahore session 1929.