Thank you for your feedback. As mentioned in the Version 37 Release Notes, Rare Titan rewards are reduced if you were not a member of the Alliance 24 hours before the Rare Titan appeared.
This change was made because some players were abusing the Rare Titan spawning logic to gain an unfair amount of Rare Titan rewards. This led to many Alliances feeling harassed by players constantly joining and leaving as they looked for Rare Titans about to spawn. This behavior also had an adverse effect on Alliance Wars because the visiting players were included in the matchmaking but never stayed for the war.
Please note that this is different from merc’ing because the Alliances were not asking for their help, and the players didn’t actually stay to help almost any of the alliances they visited.
We discussed many different options to prevent this unwanted behavior. At the time, we believed the current fix to be the best solution for the problem. That being said, we did not fully consider the effect it would have on the players who spend most of their time in a single Alliance, but periodically visit other Alliances. We appreciate your feedback regarding this topic, and will consider if we could implement a “best of both worlds” solution to the problem.