That's my thought too. "A mileage run isn't worth my time" or possibly even something they wouldn't consider but then this gives them a way to get over the hump. Or maybe someone who is within 100 MQDs would be hard-pressed to fly anywhere for less than $300 anyway so it could make sense in that scenario. But others, the spending required depending on where you are could be quite ludicrous. If you're right at the minimum bar to be eligible (or less than 100 MQDs over the minimum bar), you'd have to spend:
$1500 for 500 MQDs to get Silver
$3000 for 1000 MQDs to go from Silver to Gold
$4500 for 1500 MQDs to go from Gold to Platinum
$7500 for 2500 MQDs to go from Platinum to Diamond

The only one of those that *might* work itself out to an approximate even-exchange in the long-run relative to the purchase cost itself (and not considering that the MQDs could be acquired more cheaply by just flying) is the jump from PM to DM, if you really maximized value out of Choice Benefits (i.e. used 4 GUCs for international D1) but even then with having to buy PS in most cases to use the GUC, it's still close on whether you'd eventually break-even.

And then at the end of all of this, DL gets to take any $$$$ collected and make a "donation" in its own name and take the tax-deductions.