We could pre-load all sorts of text into a new site (we won't), but that doesn't actually help create a community to answer questions or to help curate that content.
Content has ownership, and a healthy community keeps that content updated and cared for. When you dump a bunch of legacy content into a new site, you start with a foundation with essentially no ownership — the authors are long gone, usernames are greyed-out as anonymous, voting makes no sense, meta links are broken, update notifications are non-existent… and the foundation of your site will be a collection "legacy content" which accumulates in those dustier corners you are always explaining away whenever folks notice it doesn't quite seem to "fit".
When a user asks a question, they should have a reasonable expectation it will be answered. But if you create the appearance of a big site with its knowledge imported from elsewhere, it doesn't establish that the current community is capable or even willing to answer that scope of question you are (presumably) hosting on your own site.
If you want fresh start, you need, well, fresh content. Otherwise it will just fail again. — Shadow Wizard
… and that ⤴