Okay so I believe this question must have been answered earlier but I couldn't figure it out hence here I am at it.
Why is MWF a single engine fighter. Because one of the main problem IAF raised was about the thrust of F-404 that it wasn't enough. Now MWF has F-414 with increased thrust but then LCA thehas also become MWF now and so the question that still remains whether that single engine will be able to satisfy the needs of air Force and especially Navy?
And why is it not a twin engine like the other aircrafts of similar configuration and roles?
Engines are the single most expensive item on a fighter aircraft- each one costs $5-10m USD just to procure, then factor in that each aircraft will go through 4-6 engines throughout its lifespan and all the work hours that goes in to maintaining each engine and you can understand why single engined fighters are what the IAF wants for its backbone/lower end force structure.
Almost all large airforces* have single engine fighters as their backbone- the USA has F16 (and now F35), China has the J10 etc
* Russia is probably the exception to this today and that is largely because their engines have traditionally been so unreliable although they had the MiG-21 in the 1000s during USSR days.
The Navy's requirements are legitimate and will have to be taken care of elsewhere, TEDBF?