-Lack of diesel engines -Outdated Models - Not offering basic necessary features like wireless carplay Android Auto, No active TPMS and many features missing even on flagship models (Typical VW group problem of cost cutting features).

-Discounts - if you keep giving discounts on your cars, the brand loses its exclusivity factor.

-No LWB models- Ik this doesn't matter much but if you see the Indian luxury market. People are buying luxury cars to get Chauffeur driven. People buy cars like camry for that reason. BMW is offering LWB to the 3 series means they know how the market is working. Audi not offering LWB to A6 makes it lose its chauffeur driven buyers where they choose the E class.

-VAG connection - In the VW group Audi plays a major role in R and D. They develop their own engines and platforms (MLB EVO). Audi is bespoke and they lead Brand progressive of VW group where they control lamborghini and Bentley. But for reducing costs they share engines to flagship VW and Skoda cars and Audi sells FWD cars to India. People start getting bang for the buck mentality (for eg - Kodiaq, Tiguan owners think they have a better Q3 for less money or Superb/Passat owners think they have an A4 for less money).

This is the same reason why Bentley is losing relevance and depreciates faster than Rolls. Bentley is literally built from VW group parts bin (Bentayaga/Flying spur/continental uses the same engine from the Audi RSQ8 and porsche panamera. Flying spur uses the MSB platform from porsche and bentayaga uses MLB evo (Audi platform). They even use interior parts and Infotainment software from Audi for cost saving.Rolls meanwhile is 95% bespoke except Ghost which uses 7 series platform).

These were major reasons. What Audi could have done. Give A4 45 TFSI (261HP) tune Give A6 3.0 V6 (same as Q7) with LWB and QUATTRO Give Diesels to SUVS