Within Marketing Hub, emails (and probably other assets) should be able to be included in more than 1 campaign for marketing teams.
For example, we have a campaign for our newsletters. In our recent email, we included content that’s related to a specific campaign we’re doing. However, I can only include the email and therefore the date in one campaign - not both. It helps because the newsletter is a broader campaign, yet the more niche one is important too. By limiting the number of campaigns an asset can be associated with you’re forcing us to select which one is best, not giving us the freedom to pick the places it belongs.