Are Adobe missing a trick here?
No, it's a 'smart' way to get, and keep, people on board of the subscription train. People start paying the full subscription price, because that generates more cash for Adobe faster, and the penalty for quitting
feels larger (it actually is, as well, when quitting prematurely), because it represents more 'value'.
I purchased a Lightroom 5 perpetual licene upgrade 2 years ago, if I recall correctly for something like € 80. So that has cost me € 3.33 per month over those 24 months (and I'm still able to use all features, so the cost/month keeps dropping). Early subscribers, after some hassle over reduced prices, paid 3x as much. That did include Photoshop, but I already had that (CS6), and that also didn't cost me a cent since (after the one time upgrade fee).
Now that people have 'invested' all that money in Lightroom CC through their subscription, it each month becomes harder to stop.
Cheers,
Bart