Steve really isn't surprised that it makes Loki happy. Tony is paying him a considerable amount for this.

"I guess," he murmurs with a shake of his head as he raises his glass to take another drink. "But I'm just sitting here. You're the one doing all the work."

Well, at least Loki is having fun. Steve would really hate this if the other man hadn't been. "I'm glad you think so. I don't mean to be so difficult; I'm just... a bit of a romantic, I guess."