Introduce individual awards for Clan Wars
To dramatically increase the incentive for players to consistently participate in Clan Wars, there should be some sort of individual awards that could be earned through consistent individual participation or performance.
Clan Wars has been fairly predictable in terms of clan performance. From the player perspective, this means their own participation has relatively little weight: maybe their clan needs too many wins to get to the next award, maybe their participation won't make a difference, maybe the next few clan-level awards just aren't that valuable for the player, or maybe it's simpler to just get 1 win and freeload.
Clan Wars demands a lot of players (essentially a daily chore) for currently underpowered rewards that don't have a strong relation to individual performance or participation. While Clan Wars is a clan level event, the participation itself is ultimately individual- and so incentives should also exist at the individual level.