First, it would increase your ability to search for key cards while mulliganing (say, Faithless Looting and a dredge card), because you get to see more cards on a mulligan before you decide whether or not youre keeping
Its certainly a source of income, but for a lot of artists, its worth it in other ways, as well
Note that some fake cards even don't have some of the graphics
That leads to a pile of random cards, an empty bank account, and the feeling that you're somehow falling behind
Secondly, it's mono-colour and so can more easily slot into a wide variety of decks
If you can't get the Secret Lair directly from Wizards, you might find the products on the secondary market, and a sealed one should retain all marketing components, including a potential card with your code for digital versions