I’m surprised to hear that previously this seemed to show Tweets further back than 7 days - the widgets have never supported more than that, as they sit on top of the search API which only has a 7 day index, and there have definitely been no recent changes in this area. Have you ever used a widget provided by another provider (i.e. not from Twitter settings / publish.twitter.com)? Third party widgets may well have cached older content.
In general we recommend curating timelines (collections) in this case, because you have much more control over what will be displayed in the widget - this avoids the unfortunate situations where hashtags can be targeted by spammers, and enables you to dictate exactly what will appear in the timeline. However, yes, as you said, there is an overhead in managing this.