What are the historical and cultural reasons for why there are no Divya Desams in Kongu districts (Coimbatore, Erode, Tirupur, Salem, Karur, Namakkal, Dharmapuri) when there are a lot of Divya Desams in Chola Nadu to its east and Kerala to its west?

 Historic Reasons:

1.Tamil Kingdoms were captured by Kalappirayars (read as Biharis/ Northern Kingdoms) by revolt and Shramanic religions (Buddhism, Jainism, Ajvika) were imposed. The Brahmins were executed, the Princes were Jailed and Endowments to temples were stopped. The period from 3rd to 7th century is the darkest period in Tamil History.

2.Bhakti Movement by 64 Nayanmars and 12 Azhwars revived Saivism, Sri Vaishnavism and replaced Shramanic Religions.

3.What are Divyadesams? During Bhakti Movement from 7th to 10th Century, Azhwars visited many Vishnu Temples and sung the glory of the Lord and those temples are called Divyadesams. The sacred text is Nalayira Divya Prabandham (4000 Sacred verses on Perumal).

4.Ganga Dynasty was ruling Kongu region from 5th to 10th century. They were supported by Chalukyas and Rashtrakutas who are foes to Chozhas during that time. Azhwars never visited these regions.

5.Kongu region came under Chozhas during 11th century. Ramanujar, founder of Vishistadvaitam did visit many Sri Vaishnavism Temples in Kongu region during Chozha regime.

6.Karamadai Perumal Temple, is visited by Ramanujar during 11th century and it follows rituals of Thenkalai Sri Vaishnavism sect, head quartered at Nanguneri. The temple was built by Chozhas and expanded by Tirumalai Naicker in 17th century.Maasi festival is an important festival.

7. In otherwords, Kongu is a Punya Bhoomi, came under Chozhas in 10th century onwards and hence no Divyadesam.

Hope I answered your question with the best of my knowledge.