Was there a reason for Democrats to push so hard for mail-in ballots?

There are many allegations of dead people voting in the 2020 election. Since individual ballots are secrets more guarded than transcripts of the President’s private phone conversations, we can probably never prove it one way or the other.

However, for the same reason, mainstream media’s denials of any ballot fraud is confusing. How would they know?

Plus, there are some facts that are hard to deny:

1. The Democrats pushed for voting by mail. The chances of exposure to other voters indoors is minimal and can be addressed rather easily.
2. It is definitely easier to steal mailed ballots than in-person ballots.
3. It is easier for dead people or people other than the ballot recipient to vote by-mail rather than in-person.

So my question: did the Democrats know something that the mainstream media is helping them hide?