Mostly it's due to the accused's right to confront the accusations and be heard. There is also a lot of ugly history of using trial in absentia to, for example, get rid of political enemies: quickly convene a trial and convict them while they are abroad, avoiding a long trial allowing them to make their case and forcing them into exile.
He is charged with different crimes and therefore there is a warrant out, and a request for extradition: "When he failed to appear, the Supreme Court said the contempt case would only proceed further after he is produced before the court".
There are also multiple court verdicts in favour of banks and business partners, but those are all civil law, not criminal.
https://en.wikipedia.org/wiki/Trial_in_absentia
Note that Mallya has not been convicted: https://en.wikipedia.org/wiki/Vijay_Mallya#Accusations
He is charged with different crimes and therefore there is a warrant out, and a request for extradition: "When he failed to appear, the Supreme Court said the contempt case would only proceed further after he is produced before the court".
There are also multiple court verdicts in favour of banks and business partners, but those are all civil law, not criminal.