What was the key factor that led to the formation of a coalition government by the National Front in 1989?

Support from two opposite political groups: BJP and Left Front

The 1989 elections marked a significant turn as they culminated in the Congress party's defeat without any single party securing a majority. Despite being the largest party in the Lok Sabha, the Congress couldn't attain a clear majority, compelling it to opt for the opposition benches. The National Front, formed through an alliance between the Janata Dal and several regional parties, garnered support from two divergent political factions: the BJP and the Left Front. Riding on this unusual alignment, the National Front managed to establish a coalition government, although the BJP and the Left Front refrained from participating in this governing coalition.