First Let’s travel back in time. Back in the day the winner of CW was decided based on stars. With no tie breaker whatsoever.
They then introduced the destruction tie breaker, which makes sense. Especially since it matters in more areas of the game and is a consistent factor in how the game decides how well an attacker does.
They have at that time thought about perfect wars and decided they didn't want a tiebreaker for perfect wars. They felt that if a war is perfect that both clans deserved the tie and no clan deserves to lose, therefore they decided not to implement a tiebreaker for the tiebreaker and the perfect war will just simply end in a tie. Let’s not forget that a tie is different in the game in terms of war loot compared to a loss or a win. Not that it matters to certain players but nevertheless the difference is there and matters to SC as they’ve felt the need to implement that difference.
Now whether or not something is difficult to code or not or takes a lot of resources or not is really not all that relevant. What matters most is SC’s opinion on something and if they still feel the same way then there won’t be that tie breaker even if it’s 2 minutes work.
Lastly while I personally can understand where the idea is coming from and how it came about, meaning I can understand why that could be a tie breaker. It does have certain consequences.
It will encourage some players / engineers to permanent max at certain lower TH levels. And SC doesn’t want encourage that type of play. They want each player to feel like they can freely progress as they desire.
It will also encourage people while being included in the war line-up to be excluded from war attacks or that they are told they aren’t allowed to attack anymore. Quite frankly that’s not good for the player and not good for the game and not the message SC wants to send or encourage.