It’s hard to convey why you lost because it’s often the result of a lot of mistakes that accumulate over time, such as the lack of building any income.

That said a lot of tower defenses have a sorta clear reason why you lost, such as a boss or a type of enemy you didn’t deal with properly. In BTD6, if you lost from a big zeppelin then you don’t have much single target damage. If you lost from camo bloons, then you lack camo detection, etc. It’s usually fairly obvious why you lost, and if you have multiple lanes then maybe you didn’t care for a specific one.