Really, that's fascinating. Do you have a link anything where they talk about making their decision on this basis, I'd be interested in it.
The decision to seat Michigan and Florida was made at a DNC meeting on May 31, 2008. At the time of the meeting, the pledged delegate count minus Michigan and Florida was 1636.5 - 1504.5 in favor of Obama. (In case you're wondering, the half delegate came from the Democrats Abroad primary, where each actual delegate gets a half-vote and so get counted as half a delegate)
There were 3 primaries left after that meeting, Puerto Rico on June 1 and South Dakota and Montana on June 3. Those 3 primaries were to award 86 delegates in total. So, assuming literally no one voted for Obama in those 3 contests, Hillary needed a net swing of 46 delegates to change it over to her favor.
Florida was +38 in her favor (Obama's name could not be removed from the ballot and so he was on the ballot despite doing no campaigning in the state).
Michigan was an absolute mess because Obama had removed his name from the ballot, and so the state party had directed supporters of any candidate who had removed their name to just vote "Uncommitted". Hillary's campaign asked for those results to be honored directly, giving her 73 delegates, sending 55 uncommitted delegates to the convention, and giving Obama nothing from the state. They looked at multiple options, including just halving the delegates and giving half to Hillary and half to Obama, but the option they finally settled on was to give Hillary 10 more delegates than Obama.
The rules actually mandated the half-vote penalty as the minimum penalty for the infractions that Michigan and Florida committed, and the total exclusion of their delegates was the committee trying to be serious about preventing any states from joining the group of Iowa/New Hampshire/Nevada/South Carolina that were allowed to hold contests before Super Tuesday.
Obama wanted the delegations seated in some form, because he was going to be the nominee and didn't want to piss off Democrats in Michigan and Florida, but he also wasn't willing to jeopardize his win in order to play to those constituencies. Thus, the compromise to accept Florida delegates at half-strength and the other to create an equitable split of Michigan delegates and similarly seat them at half-strength.
There is no document that you could read, because these were the deliberations of the DNC's Rules and Bylaws subcommittee, but the May 31st meeting where this was decided was livestreamed and presumably exists out there if you want to go see the whole thing. It was entertaining viewing at the time because you had PUMAs at the actual meeting losing their goddamned minds because the DNC wasn't just going to let MI and FL break the rules with impunity (which would have benefitted Clinton's campaign).