Who is doing these recurring quests anyway? Me.
Everything under the sun has a time. When an era is completed, research is done, Recurring Quests kick in to provide the player something to do until pass to the new era. In my current case, Space age Venus is not released yet, so I cant pass to the next era. Therefore, recurring quests for me. I'm farming and clicking? Don't have a life? That is a simplistic and narrow view.
In previous ages, where there is a next era already released... Is the player ready to face next era when the research tree of the previous one is completed?
Not always.
1. Some Players like to be ready to unlock all techs in one go, to be able among other things to build certain military barracks that are far in the tech tree. For that they will need all the goods/resources required by research. That may be quick for some, others will require more time.
2. Other Players may like/need to raise their GBs a number of levels to be ready to face the new era. Again, it may require time.
Time to spent in Recurring Quests can be tied to many aspects, including strategy. I have seen cases where guilds ask certain members to stay in an era longer time.